You cannot bear mistreatment just because somebody threatens to harm themselves. Inform her parents or somebody close to her about her self-harm tendencies and the fact that you breaking up with her might trigger it. Then just end things with her. You might feel guilty in the beginning for abandoning her but you'll thank yourself later for getting out if this situation.

A relationship with so much drama and toxicity is not worth it. Take her to a counselor and share your issues with them and then preferably get out if the relationship. You cannot save people from themselves. Once the relationship is over you can finally take time out for yourself and start healing from the trauma.

assure her that whatever she thinks is not true.mif she doubts you 100times tell her 100 times that you only love her and noone else....dont go out for few days..spend time with her and let her know how much you care about her..when she is stable ask her what she really wants, what made her doubt you and if at all you love each other..having trust and understanding each other is important...she loves you so she is obsessed with you...she is afraid of losing u and she has some misunderstandings maybe bcoz u are not giving her attention...talk out things and then u can decide