I know of a case where the fella was feeling neglected by his wife. Not sexually, but emotionally. She wasn't being the companion and friend he's hoped she would be. So, he stepped out on her. His "fling" was caring, sympathatic to him, and boosted his sagging ego. The sexual satisfaction he got was pretty much icing on a cake. It was also, as it came out in counseling sessions, a cry to his wife to pay attention to him, a wake up call, if you will.
He and his wife are still together, he no longer entertains girlfriends. To her credit, his wife realized where she went wrong and is taking steps to correct it, he is doing the same. The future looks good for the both of them....together!