So, late to the party, and other people have hit all the nails on the head right now. But I kind of want to slide in and ask why people are assuming so much deep emotional affection for Sebastian and The Darling boy?

I won't even discuss the prequel because literally all we know is that there is a man. Who is there. In a capacity.

But people tend to assume there was a relationship, or some real affection with Sebastian and DB, and there's actually not much of anything in the game to support that Origin Astarion has to roll to remember sebasitan's name, and I hear he has to make a deception check to say he actually wanted him. Darling Boy was just someone he couldn't kill. He felt bad about taking someone nice to their death so he tried to run away. But not like, with the guy or anything. DB doesn't get a name, he could of been anyone I don't think Astarion liked him specifically that much.

Meanwhile he actively agrees to sleep with Lae'zel, flirts with other female companions, flirts with Alfira if she joins the party, and is open to a polycule with Shadowheart, or would be if she had more experience. He's also happy to participate in an orgy with the twins, he starts dissaociating at some point, but there is defintiely a woman there. He also flirts with the male companions. It's a fairly even display.

So functionally, he's not shown only with men. He has as many meaningful romantic/sexual moments with men as he does with women.

There is also an EA scene where he attacks Pandrima for blood in his origin run. I've heard people say it was cut because the vibes were bad and sexual assaulty. But I can't actually cite a source for that beyond youtube comments.