In the U.S., if you get legally married you and your spouse get tax benefits that single people do not. I don't think it's a crime worthy of imprisonment, but fines and the revocation of such benefits might be acceptable.
I can tell you're not married. There is a whole lot more to the institution of marriage than sexual intercourse. Many people--and probably most parents--would argue that raising children together is a far more important part of marriage than sleeping together.
That one component of the marriage vows as they are customarily stated in the U.S., "forsaking all others," is probably the one most broken. The "for better or for worse" part is the most important. "For worse" includes the transgressions of the other party, including "adultery," a term so arcane that your use of it is a sign that you're probably not even an American, much less a married American. We call it "infidelity" in polite company and use far more colorful language among friends.
Lots of marriages survive infidelity.
So don't go prattling on about an institution you're clearly not familiar with in a country you're clearly not familiar with. I've lived here since I was born 63 years ago and I've been married for almost half that time so I know what I'm talking about.
If you're concerned about the inequities in the U.S. tax laws, there simply is no way to make our current confiscatory level of taxation fair to anyone. The income tax is unconstitutional anyway, and all government officials who enforce it should be imprisoned.
Not to mention that for a good many years the tax benefits worked the other way and only turned around about ten or fifteen years ago. The fact that you've never heard of the infamous "marriage penalty" is yet another signal that you're an outsider to both the U.S. and marriage.