My wife wasn't looking to cheat it evolved. They started going to lunch and talking. We were both not happy four years ago, he would be there to listen and tell her how right she was about everything and it just evolved. After time he "just understood her" in a way I didn't and provided the emotional relationship that her and I didn't have because we had a 2 year old and a new born and we were both working parents so our time together was nonexistent and they had free time during the work day. I get how it started and how it evolved what I don't get is how she could do that to me for so long behind my back and have it develop into and physical and intimate relationship.