For me...it was a whole host of messed up, entangled reasons:
- Fear of "being the bad buy" (i.e. the one who broke the other person's heart and walked away "in his time of need")
- Fear of the unknown and of breaking known patterns
- Fatigue/discouragement
- Pride (not wanting to face my family and friends who all told me he was bad news)
- The desire to fix/save/change "for his own good" (but really, for MY own good)
- The love and responsibility I felt for his son, whom I raised like my own
- Lack of money
In the end, I found I was just making excuses. I COULD leave. I just needed that extra kick in the @ss HP had to give me.