I think you are as mentally stable as anyone else on the board. We all have our good days and bad, and on our bad ones, we tend to try and take the blame upon ourselves for where we are. But actually, where are we? The old dream didn't work out. You get a new one. It may take time for it to shape and form and solify into something that you feel is 'perfect' for you, but it will.
So XH called after 7 month silence just to tell you how great he has it? Really? Sounds pathetic and attention seeking to me. Did OW know he was chatting you up like a girlfriend? Doubtful.
I think you are just on a low at the moment, and I'm sure you've read by now that those lows will become fewer and fewer as times marches on. You'll get through them, and we are all here to help.
