I wholeheartedly agree that 'no contact + forgiveness = serenity'.
I'm nearly two years on from the ex. From the moment I left I have had no contact and I truly believe that is what has saved me from the endless recriminations I would probably have gone through post relationship. I didn't know what he was doing, how he was doing, whether what happened caused change positively and/or negatively as far as he was concerned (and I still don't). He couldn't contact me and so I was saved from any quacking or blame throwing. So, the only negativity could come from me.
And that is where forgiveness comes in. Forgive as quickly as you are able: and not just your ex but also yourself. Process, learn from it and move forward.
Baby steps.. you will come through this.
Tx