What kind of abuse?
Really cheating on someone is mental abuse.
Some mental abuse is far worse then physical abuse, if the physical abuse is a slap or push that leaving no permanent physical impairment.
There is really no way to compare just random abuse against random cheating because it depends so much on the extent of what was done and even each person personal abilities and circumstances to recover
There is no real excuse for either, but abuse is much the worse.
I would say abuse is worse. When someone cheats, you are hurt, you leave and you move on with your life. Abuse messes with your whole psyche. You don't become the person you were meant to be.
both are bad. one is physical and the other is mental