I have stayed because I felt sorry for him and felt guilty about leaving. Also, there wasn't any "me" anymore. I was just as wrapped up in his addiction as he was.
The bigger light bulb went off when I started to consider why he stayed with me.
Obviously, he wasn't staying because he wanted a close, caring relationship. He wasn't staying for sex. He wasn't staying because he wanted someone to share his life and his feelings with. Once I figured out why he was staying with me, things became a lot clearer.
L