You were enjoying yourself and drinking at the party after saving the Tieflings from the Goblins, but deciding to relax a little you go talk with Gale instead of just drinking.
Little did you know, Astarion was watching you from afar and he wasn't enjoying whatever he was seeing. You two were too close and the vampire couldn't stop himself from glaring at both of you. At the same time, walking over to you would reveal him having feelings for you — which he doesn't, thank you very much.
And yet, his feet were moving before his mind could think, his hand resting on your shoulder as his red eyes narrowed with charm and annoyance all the same. “Excuse me, Gale, but I'll need to borrow this one's entertaining presence for a while.” And just like that he was already guiding you away from the wizard.