I think it may have something to do with your love for g/f. I still can't stand him and see no redeeming qualities. But that's me. I've been a lot more forgiving and understanding of g/f because you love her. I hold hope that I'll eventualy see the reasons you love her. I getting there faster than I imagined. I think it may be the same for you and him. Because you love her, you're trying to see him through her eyes. It's hard to remember why you dislike someone when they are killing you with kindness. Maybe he is changing. Maybe he was so lost in love that the only way he knew to try and keep her was to be all crazy psycho stalker freak, or maybe that's just who he is and right now he doesn't have to show it.
I'm glad you were the better man and let him invade your time. It shows her you're trying to be attentive to the needs of the group as a whole and not being selfish, as he is.
You're lack of anger comes from realizing he's not a threat. It's not oooo you're the big bad, it's that, you don't have to compete the way he does. You don't have to put on the big shows he does. She loves you for you and you recognize that.