One of my good friends is a psychologist and therapist. Back when I found out about my H's affair, I talked to him about it a bit and was told that cheaters almost always "affair down" and they look for someone less attractive/smart/accomplished/capable than their partner because they aren't threatening. They get an ego boost because they get to feel superior, and the OP really looks up to them and is grateful for their attention because they know they are out of their league.
Was definitely true in my case. When I saw the OW, H was actually embarrassed. lol
