Yes, romancing both Astarion and Gale is possible! here is how

[Xibalba]

So, here is the trick. You need to have both appreciations high. My Tav is in a relationship with Astarion since act 1, it started before the camp party. Gale has been always in my group and I had the weave scene with him during the camp party. In act 2, when arriving to Moonrise towers Astarion will approach you while in camp with his confesion scene, moment where the true relationship starts and when the kissing line appears everytime you talk to him. At that point I had 100 approval from Gale and after the scene with Astarion you can talk to him and he'll make you choose between both of them, so DON'T TALK to him all. After leaving camp there will be an exclamation mark in Gale head, again, he wants to make you choose, so DON'T TALK TO HIM. Instead take another long rest and Gale's illusion will ask you to meet him under the night sky, go with him and the romance version of that scene will trigger, allowing you to kiss him and so on.

Afterwards you can talk to both of them about your relationship and none of them will say anything about you having another relationship. After leaving camp you can still talk to both of them as romanced and ask them for kisses.

I haven't played much more after that so I'm not certain if this will cause any trouble further in the game, but I'll try this option anyway... thou I wonder how the endscene will develop.

EDIT: I finished this playthrough and yes, you can have your romance all the game long without bugs until the end. Also adding Halsin to he equation. But in the ending postscene with your romance the game used Astarion, that may be because I romanced him first or because when iniciating a romance with Halsin I chose to talk about it to Astarion instead of Gale (because if you do so Gale asks you to choose between him and Halsin while Astarion is ok with sharing).

ANOTHER EDIT: apparently this is no longer possible, they've probably fixed it.

[Xibalba]

And I just found out that you can also add Halsin to the ecuation without losing the other 2 xD

[ProestUnicorn]

You are collecting them like pokemon or something :P I tried to make a harem, but haven't tried that hard

[Xibalba]

Something like that hahaha. It's my second playthrough and I wanted to see how much you can force romance stuff, in order to do so I tried to romance all of them, but it's not easy to cheat the game that way, for example despite how much approval from Karlach I have I haven'r been able to trigger her date scene, and also had to let Wyll go 'cause Gale went mad about it. I'll keep trying just because I'm curious now to see which romance scene I'll trigger at the end hehe.

[Yamachin]

I had something similar to this one, but when Gale had invited me to meet him and watch the stars, it never gave me the option to kiss him 😭😭

[Quacksalber]

I was forced to choose between them in Act 3 although I wasn't even romancing Gale xD

[Pernesmee]

Originally posted by Xibalba:

And I just found out that you can also add Halsin to the ecuation without losing the other 2 xD

HOW, tell me your SECRETS!!! Im tryna search like a crazy person to find out how to not let astarion and helsin goooooo, i romanced with gale and now im like ugh.

[Xibalba]

Originally posted by Pernesmee:

Originally posted by Xibalba:

And I just found out that you can also add Halsin to the ecuation without losing the other 2 xD

HOW, tell me your SECRETS!!! Im tryna search like a crazy person to find out how to not let astarion and helsin goooooo, i romanced with gale and now im like ugh.

Its quite easy don't worry :)
After doing all in the first post you get to romance Astarion and Gale, after you recruit Halsin talk to him a lot until you exhaust all dialog options he gaves you. Actually Halsin is quite horny so he we'll ask you easily to have something with him once in act 3, of course he doesnt mind if you are already with another companion but he tells you to talk to your partner and seek his approval, and then you can answer him 2 options: "I'll talk to Astarion" or "I'll talk to Gale". Choose the first one, and talk to Astarion, he will be completely open and ok about it. Then talk to Halsin again and there you have it, that night he will come to you when you finish the day. However if you choose to talk to Gale he won't be cool about sharing you with Halsin and will force you to choose between both of them, so don't take that route if you wanna be with the three of them.

[Xibalba]

Originally posted by Yamachin:

I had something similar to this one, but when Gale had invited me to meet him and watch the stars, it never gave me the option to kiss him 😭😭

Did you have the weave scene with him in act 1? I pretty sure is necessary to persue his romance later in the game. And in that scene you also have to choose the right answers, if I recall correctly it was about letting him know your interest about him, like sharing a vision of both of you kissing or something like that.

[Xibalba]

Originally posted by EH!:

I was forced to choose between them in Act 3 although I wasn't even romancing Gale xD

Apparently that was a issue about Gale, he being in a romantic relationship with Tav with you didn't knowing about it hehe. But it seems Larian fixed that if one of the latest patches.

[Pernesmee]

Originally posted by Xibalba:

Originally posted by Pernesmee:

HOW, tell me your SECRETS!!! Im tryna search like a crazy person to find out how to not let astarion and helsin goooooo, i romanced with gale and now im like ugh.

Its quite easy don't worry :)
After doing all in the first post you get to romance Astarion and Gale, after you recruit Halsin talk to him a lot until you exhaust all dialog options he gaves you. Actually Halsin is quite horny so he we'll ask you easily to have something with him once in act 3, of course he doesnt mind if you are already with another companion but he tells you to talk to your partner and seek his approval, and then you can answer him 2 options: "I'll talk to Astarion" or "I'll talk to Gale". Choose the first one, and talk to Astarion, he will be completely open and ok about it. Then talk to Halsin again and there you have it, that night he will come to you when you finish the day. However if you choose to talk to Gale he won't be cool about sharing you with Halsin and will force you to choose between both of them, so don't take that route if you wanna be with the three of them.

OOF ill try it, but i tried what the first post already said and im still having issues with Astarion trying to talk about me and Gale's relationhip, he was fine once when he had a different dialogue option since something happened to karlach and her *Heart* But now he wants to talk about it so im like QwQ

[CrystalKat]

I also found a polyamory mod that i'm currently using to romance all the romance options just to get the full experience and also because my poly heart loves a lot of them xD https://www.nexusmods.com/baldursgate3/mods/1529

[Xibalba]

Originally posted by Pernesmee:

Originally posted by Xibalba:

Its quite easy don't worry :)
After doing all in the first post you get to romance Astarion and Gale, after you recruit Halsin talk to him a lot until you exhaust all dialog options he gaves you. Actually Halsin is quite horny so he we'll ask you easily to have something with him once in act 3, of course he doesnt mind if you are already with another companion but he tells you to talk to your partner and seek his approval, and then you can answer him 2 options: "I'll talk to Astarion" or "I'll talk to Gale". Choose the first one, and talk to Astarion, he will be completely open and ok about it. Then talk to Halsin again and there you have it, that night he will come to you when you finish the day. However if you choose to talk to Gale he won't be cool about sharing you with Halsin and will force you to choose between both of them, so don't take that route if you wanna be with the three of them.

OOF ill try it, but i tried what the first post already said and im still having issues with Astarion trying to talk about me and Gale's relationhip, he was fine once when he had a different dialogue option since something happened to karlach and her *Heart* But now he wants to talk about it so im like QwQ

Oh, I'm sorry to read that, I don't know what could have happened, it worked for me just fine... And also is weird that is precisely Astarion the one complaining since he is probably the most open minded companion, after Halsin of course.

[Xibalba]

Originally posted by SaitansDaughter:

I also found a polyamory mod that i'm currently using to romance all the romance options just to get the full experience and also because my poly heart loves a lot of them xD https://www.nexusmods.com/baldursgate3/mods/1529

Yeah, that mod is great, I'm using it in my third playthrough. I'm playing as Astarion and romancing everything that can be romanced hehe. I also got the good Minthara mod so she is also in the team without losing Wyll and Karlach. My camp has never been so full of love <3

[Pernesmee]

Originally posted by Xibalba:

Originally posted by Pernesmee:

OOF ill try it, but i tried what the first post already said and im still having issues with Astarion trying to talk about me and Gale's relationhip, he was fine once when he had a different dialogue option since something happened to karlach and her *Heart* But now he wants to talk about it so im like QwQ

Oh, I'm sorry to read that, I don't know what could have happened, it worked for me just fine... And also is weird that is precisely Astarion the one complaining since he is probably the most open minded companion, after Halsin of course.

Yea, Yesterday i left act 2 trying not to talk to Astarion about it, appearently because of that some romance scene did not come which was supposed to, and it messed with my game, so in the start of act 3 he got mad at me and ended the relationship, i used AGES to try to see what i could do without starting all over again, and then found out i had to talk to him about me and gale, but as soon as i did Gale suddenly got mad and heartbroken and i just sat there for like solid 10 seconds before i screamed "NOOOOOOOOO" literally darth vader scene.

So like the dedicated person i am i have now made a character only for gale and one for astarion, going through the boring act 1 to get back to where i was and trying not to mess up this time.

The one i was experimenting the 3 romances with i solely made for helsin thou, so im not too mad but i get invested in my games, so i felt morally bad for gale knowing he bonded with me in the way he did...

[Xibalba]

Originally posted by Pernesmee:

Originally posted by Xibalba:

Oh, I'm sorry to read that, I don't know what could have happened, it worked for me just fine... And also is weird that is precisely Astarion the one complaining since he is probably the most open minded companion, after Halsin of course.

Yea, Yesterday i left act 2 trying not to talk to Astarion about it, appearently because of that some romance scene did not come which was supposed to, and it messed with my game, so in the start of act 3 he got mad at me and ended the relationship, i used AGES to try to see what i could do without starting all over again, and then found out i had to talk to him about me and gale, but as soon as i did Gale suddenly got mad and heartbroken and i just sat there for like solid 10 seconds before i screamed "NOOOOOOOOO" literally darth vader scene.

So like the dedicated person i am i have now made a character only for gale and one for astarion, going through the boring act 1 to get back to where i was and trying not to mess up this time.

The one i was experimenting the 3 romances with i solely made for helsin thou, so im not too mad but i get invested in my games, so i felt morally bad for gale knowing he bonded with me in the way he did...

Oh ♥♥♥♥, that was a real mess, I'm so sorry, I have no idea what could have gone wrong... no idea.
You can go through act 1 pretty quickly if you skip conversations and do just a few sidequests, but you should definetly do some because if not when you try to reach act 2 you get a message saying that your party lvl is not high enough and that what comes next might be quite a challenge... thou that might be fun aswell if you are not playing in tactician, I don't know. However I would strongly recommend you to use mods in second or third playthroughs, there is one really interesting called "polyamory" and works great, there are many more that are interesting like "good Minthara" that allows you to recruit her in act 2 despite saving the druid groove, also there a lot of cosmetic and dice mods... and if you are worried about not getting achievements there is also one mod that alloew to get them even in moded games. It's what I'm doing in my third playthrough actually.

I wish you all the best in your game (well, now gameS) and in your romance with Astarion and Gale, both are great and really cool to experience.