Oh, Astarion is written really really well and his reaction is definitely believable.
To me it's just in really bad taste to engage in polygamy, when Astarion is already so vulnerable and uncertain. But if you Ascend him then your Astarion is also nearly stripped of emotions, so I can see that working... sort of.
He and Halsin would be an awful match, which was my point. It's not about compatibility at all.
In fact, this thread seems to prove that poly can work - with anyone but Halsin really - which is truly ironic.
(I am not against Halsin being poly, but I don't think the poly options make sense for anything other than to scratch an itch - which probably bothers me more because I am demi.)
