Manipulation, threats and control

The question is deep and complex, but you give no background to your particular situation. So I can only give you a "textbook" answer, that might not fit well to your particular situation.

The real key here is maturity. Not on the manipulator's part, since he or she is not acting maturely. Rather on your part. By maturity I mean taking responsibility for your own actions and emotions, and putting a boundary between you and the manipulator.

The message implied here is: I love you, but I cannot control you or your actions. I certainly will be upset if you harm yourself, but I cannot control you and I do not want to control you. Ultimately, it is your choice to harm yourself or not. If you think you will harm yourself you should go to the hospital. Since I care about you, if you need that to stay safe, I will help you with that. But I will not control your behavior, and of course, I can't let you control mine.

You have to be ready to stand your ground and not be controlled and not be controlling. Both sides are important. It is also important to be ready to call 911 if you think that the person will harm themselves or the person asks you to make the phone call (even if you think he or she is "testing" you.)