I'm not even sure if cheating is the most hurtful thing to do to a partner. What about if they don't cheat but they abuse or beat you? By getting abused/getting beaten, there is no respect, trust nor security either.
I think I'd rather deal with dumping a cheater than getting a restraining order against an abuser. They can also tend to stalk you if you try to leave. Fearing for your life and/or safety has got to be the worst feeling ever, more for us women.