I've always had the option to say I'm with someone else...that's strange.
I always romance Astarion and our romance officially triggers in Act 2 (with more official stuff happening in Act 3). So that might make a difference.
When I do, Gale gets upset cause he felt something between us and says "It's Astarion, isn't it?" And I can tell him yes.
From then on, the only people who proposition me are Halsin, Mizora, and The Emporer.
When that happens, every time I have the option to say "Sorry, I'm with someone else" and Halsin even says "Yes, I know you're bonded with Astarion..." And then he goes on to suggest he wants us both but ya know, that's Halsin for ya.
Either way, it might be different because of when you get your "official" status and since Astarion makes us a thing in Act 2, that sounds like it's a lot earlier than SH.
