OK, all this guilt and mea culpa is a little strong for my stomach. Especially in the morning.
Retrouvaille can only help you, cause they don't make you do this stuff. You talk about what you did wrong briefly, apologize and move on. It is garbage, the worst kind, and it breeds unhappiness the way garbage breeds flies. You have to stop dragging it around with you everywhere you go.
As for your memories, I believe you will find them too. I forget how long you say you were married. But I'm sure you have a wealth of good memories -- you just buried them. It does help when you have an affair, not to have good memories of the marriage interfering. And this is something you should at least start to touch on at Retrouvaille. But it would be a good thing for you and your husband to discuss things like -- What was the nicest thing you and I did together? And how do I feel about that? Or, Think of a time when we were really happy together, how did it make me feel? These are better thoughts than all this guilt.
You've got a long time til July. You will have to move your thoughts out of all this sifting through the sewage of your lives and into the good times.