Sometimes lonliness can feel so bad that a bad relationship feels better than no relationship. You'll have to decide which is worse.

He is who he is. His bad behaviour isn't all due to drinking. He's very immature. What other options do you have for being socially involved with others. It sounds like he became valuable to you because, without him, you are too much alone. Make yourself less dependent on him for emotional warmth.

If your therapist has become the closest thing to a good friend in your life, then that is your biggest problem. We all need other people . . . not just one romantic interest who becomes everything to us. There needs to be more deposits into our emotional bank account. Your account may be low, so he becomes excessively important to you.