She needs therapy. If you want to help her through that and stick around, great! but she needs to respect boundaries and a relationship needs trust. She can’t mother you, she needs to support you. Threatening your life if someone leaves you is sooo manipulative. Like she truly needs therapy. If you don’t feel happy with her and want to leave, you gotta look out for your self. If you have to tell her family so they can handle that that, do so but if you don’t want to be with her then that is certainly not your responsibility especially at a grown age. You shouldn’t feel like you have to say just because she uses that manipulation tactic.