I can only imagine how tough that can be, especially because you've had a history of problems on top of it. I for one haven't been cheated on, so I realize I may be making this sound easier than it really is, but you can't let this eat you alive, you must try to move on. The toughest thing to do when you're depressed is to see the glass half-full instead of half-empty, but if you continue to let this problem and these visuals take over your life, you're going to have a harder time coping later. Your best step right now is to keep talking with your phychologist, I hope you find a solution that works.
Best of wishes to you