Social punishment for cheating, is often social isolation. I don't think a minor victimless infraction warrant said punishment. And the fact that there's another person who has the right to consent on your own body sounds very iffy. Also, we treat "monogamy" as a natural thing. it isn't. if it was, there would be no divorces, breakups, or affairs. Also the state and religions push monogamy as the upmost important relationship in someone's life, rather than community, which atomises people and destroys communities with the modern invention of "nuclear family". where evey need is comodified rather than being provided by a community.