Could be the "guilt". Or the uncertainy of being able to "perform".
When my H was seeing the OW he had problems keeping an erection, I thought it was his meds, but it wasn't, it was the guilt. After the bomb, our sex was WOW!
But since he left we have not been together. And we are know getting a D. I wanted to try, but he didn't.
I don't know of any books on it other than Michele's but keep searching, there has to be a solution out there somewhere!
WOW!