Get out now.

No matter what you do, it WILL end badly. It is just a matter of minimizing it all.

If she threatens suicide, call 911 and tell them what she told you. Even better if you have the evidence via a text or on a voicemail, as it would be proof and more than just you getting pissed off and trying to get her committed.

Change your phone number. We all know that call block is a joke and it takes 2 seconds to get around it.

If needed, get a restraining order.

It may sound like these are harsh measures, but you really do need to assert your boundaries so that NO means NO. Right now you are letting her trample all over you and by taking her back, you are telling her that her behavior is acceptable. That is, her bad behavior is getting her what she wants, so she has no incentive to change.