SCH - I understand that he doesn't want to be blamed and reminded forever of what he did, and how wrong it was. Just him bringing it up shows me that he is ashamed of it.

You can try to validate this way - "I understand that you needed to leave to sort things out and to give us space. We can now work on our relationship and make it better then ever".

You don't have to explain to other people who did what and assign blame. If they ask tell them that it's between the two of you and that you are both working on it.

M53 H54 D17
M33Y T38Y
Bomb OW 09/09
OUT 10/09 BACK 11/09 OUT 01/10
WANTS TO R 04/10 BACK with OW 05/10
Wants to Reconcile 05/11 I said NO