Seeking expert testimony is a sign of strength. A personal relationship with a caring professional is proven clinically effective.
It seems as if your relationship started to deteriorate some time ago when you began to lose your desire for her, as a result of constant bickering. The relationship was already failing, and inevitably you both cheated on each other. Each of you have admitted to one affair. You only admitted because you had to because of the STD, which could have come from the stripper.
It seems that you feel that what she had done is worse than what you had done, but as an independent professional observer, they seem equal to me, and it is a mistake for you to try to take the relative moral high ground.
If you want to continue this relationship, if you truly love each other, then you will have to start with mutual forgiveness. If you truly love her, then you must find all of the grace in your heart to give her what she needs, and that is for you to move on.
She must do the same for you. You must forgive and never bring it up again.
Now, we have to discuss the fact that this obsessive thought remains stuck in your mind and keeps haunting you.
There are techniques for thought stopping that really work. Rather than to give you a 10,000 word treatise on the the subject, let me recommend a wonderful book that can explain you much more succinctly on just how to do this and rid yourself of these thoughts:
I would also strongly recommend a book about couples communication. This is the best book on the subject, bar none, for married and dating couples who are serious about establishing a good and honest relationship (and who wouldn't?).
I believe that the first step is to stop holding on to these thoughts in conversation and cease talking about what happened. It is done and in the past, and talking about it is like stirring up a cool clear spring: you stir up all the silt and muddy the water.
Purchase those two books and work on yourselves and on each other.
I wish you great success in restoring this relationship and to that end I shall keep you in my prayers.
Elliott, MAE, LPCC, NCC, CCMHC