Speaking of Karlach and all the extra stuff in her origin. Astarion even has unique lines gushing over Wyll in Karlach playthrough.
I actually find this surprising because in my game he and Wyll were only bickering and dunking on each other. Astarion seems to have the biggest rivalry between the other dudes for Tav's affection and he sounds the most jealous and cynical when saying 'new, true love' when speaking about Wyll and Gale. Then there's the whole Halsin thing. On the other hand he says he'd be ok with a poly arrangement with the ladies but won't do it because they're too fragile (Karlach) or inexperienced (Shadowheart).