Rain, you handled this beautifully. The most important thing is you didn't allow your desire for R to cloud your judgment and accept a relationship that was outside of your boundaries.
Agreed he will cheat again. You don't have to explain it to us. This was beyond evident reading this exchange.
The one thing I'd like you to do is forget about trying to win the argument with him about who made the choice. You aren't going to convince him. If he felt cheating was making the choice to leave then he wouldn't have cheated...but since he wants to cheat he has decided that shouldn't be a deal breaker so he isn't going to change his behavior and thinks it should be ok, so he considers you the one leaving. He truly feels that your not accepting infidelity is walking out on him. Which I guess it could be, some women accept lifelong infidelity. Whatever.
Point is, you're not going to convince him...and you shouldn't need to. Why do you need your WAH to validate you? Why do you need him to acknowledge he is wrong, you are right, etc? First of all that may never happen. XW's narrative hasn't cracked in the slightest in 1.5 years, my IC said it could be 5-10 years or never before she questions her narrative. So don't hold your breath. But secondly, even if you get validation from him, that's not a real win...a real win is getting to where you don't need it because you get your validation from YOU.
Anyway, thanks for sharing, sorry he's such a jerk, and keep posting. Your work is not done.
Me:38 XW:38 T:11 years M:8 years Kids: S14, D11, D7 BD/Move out day: 6/17/14, D final Dec 15