Early in our marriage, about 3 years in, I had a full-on PA. I ended it due to guilt. 4 years later I confessed it to my H. He said he would forgive me and we tried to move on. But we never had counseling or did anything to try to work they the "whys" of me having an affair. Also, we BOTH just considered me a sinner. We BOTH assumed he had made no mistakes, it was all just some flaw within me. In retrospect, this was the nail in our marriage coffin.
