I'm going to leave my girlfriend for the sake of my own mental health even though hers was worse
Why do you think your mental health is more important than hers?
I don't want to be with someone that is making me more sick and unable to control things.
It might be mutually beneficial if you break up with your girlfriend. It sounds like she causes issues for you and it is probably the same for her as well. It sounds like the healthy thing to do.
I bet I'll be extremely happy.
It's good you feel that way. I bet you both will be a lot happier. You need to find someone more stable that you can lean on.