It's like having an affair with Minthara and constantly fighting and provoking her, including calling her names of those she hates (Cazador in Astarion's case) and hate her possessiveness 24\7.
But there's also the problem that Astarion's evil isn't revealed enough. His evil past as a corrupt magistrate, whether he remembers it, whether he regrets it and also it's all bound to depend on the playstyle, with an evil player Astarion won't hold back, his dominance in romance is also poorly exposed.
