Me, and Wolf are both men. As for injury, like you'd have to really go at his ass to do that lol. I'm saying if you put your penis in someone's mouth they probably won't be harmed. Yes we could go final destination shit, where ridiculously implausible but technically possible things like drowning in cum happen, but let's be serious. The main damage of rape is emotional social. You were violated so now you are emotionally hurt and there is psychological damage, and you might be sanctioned socially either seen as less than, or are seen as "sullied" or whatever. Most of the time it's not physical damage like if I punched you and knocked a tooth out.
Fair, I get where you're going here. But the thing is, words by themselves can cause emotional/social harm as well, and those are legal. Actions done with others can harm people for irrational reasons too. So we need to be careful that when we define the justification for laws, we don't use a justification that will allow mean words to be banned as well.
The difference with rape is that there is a physical component. Yes, it mostly causes mental harm, but the immediate harm (by which I mean violating of consent) is physical.
Adultery, meanwhile, could justifiably be at most breach of contract, as yes, you broke a contract (relationships and cheating on non-marriage ones still break an oral contract as well, so those could be argued as well).
I might be willing to agree to such a compromise as long as the government allowed ANY terms in the contract not just what the west allows. So if both me and the other party agree that whoever violates the contract that party will be executed. Would that be ok in your thought experiment?
Generally, I believe most contracts need to be exitable. For your health, I'd recommend it, as it incentivizes spousal murder and other abuse to an insane degree. That's not a moral requirement, to be clear, just a common sense one that a lot of history has shown to be worthwhile: non-terminal contracts are no good. Its the same reason voluntary enslavement is banned as well: too exploitable by the powerful, and lends itself to abuse and problems.