You're not stupid and you are not super-human and you are not weak, as has been mentioned you are grieving and that's normal.
Breaking up, sometimes, with an alcoholic is not like a normal break-up in many ways.
If you look at the man as two people. The kind, loving, romantic, etc person that he can be - Man 1 and the abusive, mean, person that texts you when he is drunk - Man 2, how tough is that. You don't want anything to do with Man 2! He is horrible! You don't deserve to ever be treated like that, you only want Man 1.
Well Man 1 does not exist, anywhere. He is one person, the good and the horrible.
Even if he got sober, those problems he has may well remain, there is a reason he drinks to excess, there is a dark side there, based on what you have mentioned.
Did you tell the therapist what he has texted to you? I hope you will, if you haven't already and I mean all of it, the worst of it, get his viewpoint, I think that might be helpful. Perhaps writing it down and taking the list with you would help.
I don't see any mention of him quitting drinking at all? Has he not even suggested that? That and getting help?
What is all this about taking him for granted? Because you can't accept his abusiveness?