To get back to topic: I'm trying the Astarion romance atm and somehow managed to get a high approval with him for the first time ever - and I'm playing a really good character, so I must have done some dialogues right, because I get a lot of dissapproval from simply helping people.
Astarion is stupid easy to bed.
I played with four custom characters which means he never was in my party. I made all “good” choices and pretty much ignored any approval ratings. After defeating Minthara, everyone else rejected my character. Not Asterion.
With the right combination of dialogue choices, I got the romance scene.