Star Crossed Lovers

[Xanoth]

Is there a way to complete the quest (make it go from the journal) after you promise to keep their secret and without betraying them?

[Raynezazki]

Yeah this is exactly what I was wondering. The only way to complete the quest being getting them both killed is just...eh =/

[Gandalf of America]

Looked around, it appears that there are only two options to finish the quest: tell Gruntilda and they die, or finish the quest War of the Stones and they kill each other
of course, if you don't do either of those things then they'll just sit there until the end of the game,