I think for years I blamed myself for my ex becoming a bad girl
That sounds rough. Why do you blame yourself for that?
I wasn't supportive enough when she was in trouble.
You shouldn't blame yourself for other people's issues. You need to understand that you did the best you could.
I don't think I did the best I could. I should have stuck out with her.
You can't change the past, and it's great you see the errors in your ways. But I believe it's not healthy to continually beat yourself over what you couldn't do. How about using this as a learning experience, so you can enjoy your next relationship to its fullest?