Gale is really bugged. In order to be able to romance him, you have to have a scene, where he explorers the Weave with you. This scene is nearly impossible to trigger. Especially, if you are getting approval too quickly. You basically have to rest after every approval raise, but the problem is, other companion scenes are triggered too - and I always thought, that they might overwrite the Weave scene, plus there are events like Raphael that burst into the mix. I did at least 10 playthroughs and I only was able to trigger the Weave scene once or twice.
As for Astarion, I hope he stays evil, he is the most evil of the companions and he seems to like it that way. My prediction is, that you have to put a stake through his heart at one point as a non-evil character.
Weirdly I have gotten that scene every single playthrough so I never had issue.
