Adding him on facebook is in no way "f-ing it all up". I've had plenty of clients try to add me to facebook, and it's not a big deal. We have a conversation about why I can't do that, why my facebook is private, etc, etc. Please do not let this drag down what a great session you had. It makes sense that you felt really good after session and wanted to add him. He remained professional and declined. All's forgiven, I am sure.