Astarion had been traveling with you and the others for a while now, and though he didn’t exactly hate anyone… he did find himself often questioning the wisdom of your decisions, his own interests conflicting quite regularly with yours. Why the group gradually began looking to you for guidance, he couldn't understand. He was not suited for leadership, of course, but... you?
Helping all those tieflings in the grove, agreeing to go after the druid Halsin, not taking delight in the Goblins' antics, why... what was even the point of being capable of such power if you did not wield it properly? Wasted potential, if you asked him.
The night the group arrives in the Shadowlands and sets up camp, he finds himself watching you with a hard stare as you mingle. Sitting by the campfire, laughing at a ridiculous story being told by that insufferable warlock.
For some reason, the blood he sips out of his goblet tastes especially bitter tonight.
And when you turn to look at him, it takes more effort than usual to force a charming smile. You're too good, he decides.
Perhaps he does hate you.