SOA, Don't give him all the details of what you discussed w/ the online dudes. Just acknowledge that you know you did wrong and you know that it hurt him and would do anything to take it back/wish it wouldn't have happened/own it, etc.
He knows what I did with the online dudes. But yes, I know I was wrong and I would do anything to take it back, and anything to salvage our relationship, and piece our lives back together.
