@Van'tal Without spoiling the game for you: there is at least one instance where he approves of Tav torturing a man, another where he encourages Tav to submit to being tortured for his pleasure, one where he confesses that his master had them both submit to torture and to torture others...
...for me, it's a wonder Astarion is still (somewhat) sane but also able to fake being normal for so long.
He's traumatized and I feel bad knowing what he went through - and still going through - but he's still a elitist, racist, sadistic, deeply disturbed individual.
Like GM4Him mentioned in some of his posts, in PnP, if he didn't fake it (and fake it better than what we get ingame) players would see such NPCs as dangerous or untrustworthy... and either kill them or refuse to take them along.
(But he's got a good VA, his stats are good, his bite is good, his character design is sexy, so until he tries to kill Tav for real - not these half-assed attempts, he's staying with the team. He's a sort of... disaggreable, morally-revolting eye candy. Like Lae'zel.
There's a stake with his name on it if he ever tries to betray Tav&team to Cazador; ...though being able to put a boot up his arse whenever he starts with the racist remarks would be such a plus. Larian, please!)
Spoiler with locations:
Shattered sanctum - guy on the rack; Shattered sanctum - priest of Loviathar; Camp - talk after bite;
