I am surprised that you paid the entire Retro fee upfront. My experience is that they only take a deposit up front and ask for the remainder at the end of the program. I feel certain that they would refund most if not all of the fee at this point. You are not the first couple to cancel, and there are always last minute people who want the place you are giving up.
But.....you and your husband have severe communication problems. And Retrouvaille is ALL about communication. There is no reason that you have to go with a mind to reconcile. If you can go and learn the communication skills, you will get more than your money's worth from the weekend. Communication is essential whether you continue together or separate. What the two of you are doing now is not working. The weekend would help you. Just take the focus off reconciliation.
