We don’t have enough jails to enforce this idea!

lol
I don’t think it should be a crime, although I have been reading lately that spouses of adulters are now SUEING the other spouse and/or the person that they cheated with!
Sadly, marriage for some people have become nothing more than a piece of paper likened to a rental agreement that you sign when you rent an apartment and not as a lifetime vow before God.
I don’t think it would keep a person from cheating either or jumping into marriage. At the time when a person gets married they’re thinking that everything is “coming up roses” and there is NO WAY they would cheat on their spouse. No one ever anticipated being cheated on so the couple will probably not even take it into consideration when getting married.