Therapy for any addiction is a rough road - and, it's often suggested that members not be involved in relationships at the time they're trying to clean themselves up. So, he may be confused by how to proceed - thinking that he can't focus on both his treatment and his relationship. Especially in the beginning, it can be very tough to have to own up to how much hurt he's put you through. My guess is that his therapy is forcing him to truly focus on some of his destructive behaviors and the guilt is getting to him. This is a natural response - especially if it occurred right after a session.
All that is to say that I don't think he's 'making excuses,' per se. I think he may just be having a hard time looking at the pain he's caused. If you can pull back a bit and let him 'vent' about it, without feeling like the relationship is threatened, it may be better. Have you spoken since his initial texts? Did he say he wanted to break up, or just that he was worried about hurting you?