(((((((Christi)))))))
I'm sorry you're having such a hard time with your stepdad. It's hard to watch them continue to use and be consumed by addiction. I'm sure you've heard the saying by now: Nothing changes if nothing changes. And while his reasons for getting high don't have anything do with you, he turns to you afterwards for help b/c he knows you'll be there.
The only one you can change is you. And believe me, you will change when the pain of living the way you are is worse than the pain of changing. Detaching is hard, especially with the fear of what might happen if we're not around to catch them all the time. But this is all about you. Only you can save yourself, and your parents are the only ones that can save themselves.
Take care and hugs,
JG