I don't think a healthy proper relationship is what Astarion is strong at. Tav picks a vampire who likes murder, power, control and gives him everything. Because Tav is evil and wild like him, so she doesn't care what kind of thing Astarion does - in most cases. Tavs who choose Lord Astarion and say "yes" multiple times don't think about a healthy relationship at all. Evil in that sense.
I can turn on a 15+ Japanese romance where I am clearly told and shown that all is well and will be well, these two vampires love each other, care for each other and will not let each other go. She is not his equal and can't leave, but he is into that too. They have a special, unique bond forever, enjoy. 15+ Not because it's for little ones, because complex Dark Romances with love-obsession are for adults. It's for little ones where they're taught what's right\good\health and "wrong", "don't do". And in already 15+ people are considered savvy in Japan.
