I went to Retrouvaille with my H, and it was great! It does have a very high success rate, but with 2 conditions:
1) Both spouses must go with the intent on *trying* to work on the MR.
2) There should be no involvement with outsiders (EA/PA).
I encourage you to make plans to go. Be aware they will have someone call both you and your H and ask about your intentions and about any ongoing affairs. The weekend is hard work, but VERY worthwhile, so go if your H is still agreeable to going. But set expectations accordingly, since you have that gut feeling that there is likely an EA going on.
At least you will know for sure where things stand afterward. I will pray for your sitch and that things turn around.
