premedbails, you made the right decision! It's sad your ex is such a mess so early in life but there is absolutely nothing you can do about it. It's all on him to seek sobriety, or not.
I was also involved with an addict/alcoholic in my college years. I came within 6 weeks of marrying him. He'd been in a program and was clean about a year. Then he had a "couple of beers" and I cancelled the wedding. (I was 20, your exact age.) I'm shortening this a great deal but the point is, leaving him was the BEST decision I ever made in my life and that decision was almost 40 years ago.
Let yourself be sad, cry, do things that make you happy whenever you can. Wake up in a clean, dry bed every day for the rest of your life. You will heal and you have a good, long life ahead of you. Learn from this and never date an addict (to anything) again.
It's great you found SR. Read the stories of life with an active A. You're not alone.