i want to play this with my gf. am i supposed to buy two copies?

[Fatal AR]

title.

[Slaywee]

It depends where you and your gf are? If she has her own steam account then she might want to buy a copy for herself. But if you guys are living together in same house then you can play as co-op mode or remote play together.
I am not sure but I think you can also use family steam option to have your games install in her computer or laptop as well. I heard about this but i never tried it myself but I'm sure about steam family option. You can give it a try.

[Nibbie]

You have several options depending on your situation.
Living together:
1. This game has couch coop. Plug in controllers as needed for extra players, or I think you can split the keyboard as well.
Living apart (or want to use your own computers):
2. You can use the online function by both buying the game and inviting each other through Steam.
3. You can use another program, such as Steam's Remote Play Together or Parsec, to simulate couch coop from across the internet, allowing you to both play on one game as if you were sitting next to each other.

[Vixc]

steam remote play, u two can paly as long as both have controller