It sucks. I was with a woman that felt the same. In my good bye letter to addiction. I wrote that i drank and smoked to be social and have fun. But it was always me and not the substance.
I believe life is about learning from mistakes. The healing of time and knowledge of self. Too many people hurt people with their emotional baggage.
Cheating is another form of escapism. Be strong. You will definitely find something better.