You sound like a very smart lady. Going to his parents was the right step to make. They are now aware of the problem. An intervention is a good thing and if he doesn't at least admit he needs help, then......yes, leave. You are young and have your whole life in front of you. A guy is usually on his best behavior in the early days of a relationship, so if you are seeing this now, imagine what the future will hold for you if you stay and he doesn't get help. It will only get worse.
If you know how to contact the old girlfriend, I would and ask her if she saw this in their realtionship.