Separation excuse

So how do I, the betrayed, handle his thinking that because he just left me a note, moved out and "separated " it was not an affair? Within 3 months he was sleeping with his married receptionist and then she moved in with him at 4 months. I would still see him, talk, but he never mentioned her. After 8 months I figured it out and confronted him. He admitted it. We got back together, she married another that she was also involved with, but he has not committed to getting help himself after almost 4 years. I'm at my wits end if we can ever truly get through this since I'm still stuck in the discovery process. He said he would join the boot camp with me but has yet to do it. I'm on day 2 by myself. What will make it click for him? He wants us to be together so I just don't get it! I'm completely frustrated and just want to move on or call it quits.