Heyo I have something similar. Never have much interest when it’s “my turn” and I get most of my enjoyment from getting the other person off. It real does cause a lot of intimacy issues when unaddressed. Drug and alcohol can also REALLY take the punch out of it all. He’s stayed with you this long and is open to talking to you about it. He obviously cares about you. I would really try not to take it personally and see a therapist. Maybe as a couple. Maybe individually. It most likely has nothing to do with you and he may actually feel a lot of guilt surrounding it. Seeing as a man’s sexual performance has so much weight behind it socially.