Your shrink told you that quote, that cheating is normal? I would have sought a new one. Cheating isn't normal, not if you truly love someone and not when you commit to one another in marriage. That's a shitty shrink.
She meant, it's normal as in it happens to a lot of people. It's not considered a mental disorder. It doesn't make someone a deviant. I had viewed it as something someone did if they were mentally fucked in the head.