I don't really see how asking someone not to do something that you have already discussed as hurtful, and is more than a bit over the line of infidelity would be considered controlling if someone is in a monogamous relationship. If the relationship was an open one yes that would be controlling but if you have agreed to commit to each other then commit and if you cannot then you probably shouldn't be in a committed relationship. It is not at all abusive or controlling to insist that someone does not cheat on their partner. The op considers this to be tantamount to cheating and who are you to suggest otherwise?