First off, well done on all the progress you've made- seems like you've come a long way since you were last on here!
It seems like you know that you need and want to end the relationship, but I can very much understand your fears about the implications of leaving. I don't think that is reason to stay though, and ultimately that probably isn't what she'd want either. Does she have any mental health support at the moment? And what about family/friends? It would be nice (and also give you peace of mind!) if you were able to let one or more such people know that you are ending the relationship so that they know that they will need to be there for her and help her work out how to manage things without the support of your relationship.
I think it is possible to keep someone in your life as a friend post-breakup, though I think for me it worked better to have a bit of a gap in between, especially given the added complexity of mental health problems being involved.
If you have any questions feel free to PM, as I think I've said as much as I'm comfortable sharing on the public forums now! (My ex, who remains a friend, is a member of this site so don't want to say too much).