Ian:
1) Please talk to someone "real" in your life. This message board cannot do anything physical to help your situation. Try a counselor, neighbor, older friend?
2) I agree that you are too young to be using message boards, however, I understand your need to do so... again, tell an adult what has happened.
3) I will not take sides on which parent is right, which is wrong, who did what first that led to what.... what your mother did was very dangerous, but no one can know why she felt such desperation. I don't know, and you probably don't either....nor should you have to know. They are both your parents, you have a right to love them both and be loved by them both.
4) Nothing is your fault or your responsibility. You are allowed to be 13, have your own life, and your parents are the ones who need to take care of YOU, not the other way around. It's NOT YOUR problem to figure out. TELL someone, get some other grown up to deal with it.
5)If you really want to "do something to prevent this type of thing from happening"....FOR YOUR OWN SAFETY, go back to number one again. Please do it. You are in a sad situation that has nothing to do with you. Continue to love your parents, however faulted, but protect yourself now.