You CAN benefit from this mess, you really can.
Your relationship CAN be better than it was before the affair, but not without an awful lot of effort, the whole truth and a lot of time, patience and rebuilding of trust.
This is not YOUR mess to sort out, this is HIS doing. True both of you will have to work really hard to get past this, but WE did not have the affair HE did.
WWIFN was great at picking apart the affair and getting the OP to identify the anatomy of the affair, when he started to pull back, when he gave himself permission to cheat, how he conducted himself WRT you and the DC during the affair and how and why it ended and his behaviour to all parties. You need to look really hard at events that lead up to this, it'll really help you to identify where your marriage became at risk from infidelity, and why, and then how to strengthen the relationhip to prevent it happening again.
He needs to be truthful with himself first, and know why he ended it. He has to tell you that truth too.
WE are not willing to just give up on this, but HE was, cos HE chose to sleep with someone else, surely you don't have to be a Rocket Scientist to think that doing this could end your marriage?
You both need to do lots more talking, lots more truth, and who knows, maybe you will come through this.