exgirlfriend you should really take your ex's advice and forget about him. No matter how hard that is. Abusive people whether they are on drugs or alcohol always remain abusive. That's strictly been my opinion and experience.
If you ask me him having a drug problem is the least of his problems at this point. People who feel that they have the right to degrade, put down, trash and be mean to others have ALOT of other issues.
I was married to an abusive spouse for almost 10 years. It took alot for me to endure that kind of pain. In fact that pain was far worse then leaving him. I felt victorious when I left that relationship. Any person who wants to see you suffer more than being happy in life is a waste of time.
Pick yourself up and get into some counseling. Ask for help. There is power in getting the knowledge you need to get through this. I really hate to say this but if you dont learn it now while its early in life you will wake up in 20 years with the same kind of turd laying next to you and your asking yourself "why does my life suck so bad"! Just my opinion.
Prayers to you. Good luck in whatever direction you go.....