Personally, speaking from extensive experience, I don’t really care about infidelity. We’re a semi-monogamous species, after all (the evidence for which is overwhelming, and I’ll write about it in an article here on Medium sometime). What I do care about, however, is the lying that the typical vanilla couple resorts to in order to hide infidelity. Lying is corrosive, toxic, the kiss of slow death for an intimate relationship.
Maybe if we weren’t so obsessed about sexual fidelity we’d be less likely to make our partners feel they’re in a kind of sexual prison. After all, we can become obsessed by what we’re denied, even if we didn’t much want it when it was openly available. I much prefer to be with a partner who’s happy and open with me and who has sexual experiences with other people, than to be with someone who’s secretly hiding her feelings and thoughts because we’ve been told by supposed authority figures that we have to be monogamous.