YES you did the right thing. It's sad for sure but this isn't your problem to fix - even if you stayed and no matter how much you love her. There is nothing you can do. It is totally up to her. Maybe she'll find her way out, maybe not.
I was with an addict when I was in college. All the love in the world didn't stop the abuse, the theft, the nonstop lies and broken promises. We had times of sobriety, even over a year at one point, but in the end I didn't want to live my life always waiting for the next relapse. After four years I left and it was the best decision I ever made.
You sound like a really nice guy. You have your whole life ahead of you. Learn from this and make good choices. God bless.