The goal of a law is threefold: 1) Punish those who endanger societal cohesion, 2) make right the wrongs caused, and 3) discourage others from breaking the laws in a way that doesn't make them break even worse laws.
Adultery is, at its core, a tort law infraction. You sign a contract to be faithful, and then breach of contract occurs. At-Fault Divorce, pros and cons, have already been discussed here. But does that right the wrongs caused? You say "emotional damage", but then if you put a dollar value to it, that isn't fixed with a paycheque, or with a lack-of-paying-them-cheque. The most you could get is reimbursement for costs for therapy. That would be righting the wrong, after all, but I have a feeling "people who provably cheat on their partners, need to pay for their partners' shrink" is not the law you're seeking.
So emotional DAMAGE... Like Emotional Violent Battery. In New York, that would mean if you cheat on anyone twice, you're in jail for 10 years MINIMUM. A third puts you away for 25, minimum (according to a quick Google search). Well, that certainly fulfills requirement "1", but it doesn't right any wrongs. But many felony charges don't do so, so it's not too important. So "3": If you cheat on a man, you get 25 years. If you KILL a man, you get 6 months, maybe a year. That DEFINITELY goes against the idea of discouraging breaking laws in a way that doesn't make you break worse laws. You'd be making a pile of corpses since the penalty for murder-but-self-defense-but-reasonable-doubt-it-wasn't-self-defense is so much lower than the penalty for adultery.
So really, the issue is our current legal framework doesn't have an idea as to how to ethically enforce such a law, if At-Fault-Divorce (Which isn't a criminal illegality thing) isn't good enough.
The emotional damage can be significant, true.
So... What?
The goal of a law is threefold: 1) Punish those who endanger societal cohesion, 2) make right the wrongs caused, and 3) discourage others from breaking the laws in a way that doesn't make them break even worse laws.
Adultery is, at its core, a tort law infraction. You sign a contract to be faithful, and then breach of contract occurs. At-Fault Divorce, pros and cons, have already been discussed here. But does that right the wrongs caused? You say "emotional damage", but then if you put a dollar value to it, that isn't fixed with a paycheque, or with a lack-of-paying-them-cheque. The most you could get is reimbursement for costs for therapy. That would be righting the wrong, after all, but I have a feeling "people who provably cheat on their partners, need to pay for their partners' shrink" is not the law you're seeking.
So emotional DAMAGE... Like Emotional Violent Battery. In New York, that would mean if you cheat on anyone twice, you're in jail for 10 years MINIMUM. A third puts you away for 25, minimum (according to a quick Google search). Well, that certainly fulfills requirement "1", but it doesn't right any wrongs. But many felony charges don't do so, so it's not too important. So "3": If you cheat on a man, you get 25 years. If you KILL a man, you get 6 months, maybe a year. That DEFINITELY goes against the idea of discouraging breaking laws in a way that doesn't make you break worse laws. You'd be making a pile of corpses since the penalty for murder-but-self-defense-but-reasonable-doubt-it-wasn't-self-defense is so much lower than the penalty for adultery.
So really, the issue is our current legal framework doesn't have an idea as to how to ethically enforce such a law, if At-Fault-Divorce (Which isn't a criminal illegality thing) isn't good enough.