If one has an affair on their partner, aside from the morality, guilt and violation of trust ( not to dismiss these variable), what is the over-riding issue to be taken away from this?
I think monogamy is a social construct. Some people crave it and some people don't. I have been in completely monogamous relationships, completely open relationships, and relationships that fell somewhere in between. For me, monogamy doesn't matter as long as I can trust my partner to use protection and not bring home diseases. All I really ask for is honesty.
The partner is probably lacking something you need.