It sounds like you're being abused by your girlfriend. This is a pretty classic case of emotional abuse and WILL escalate. You have done the right thing by communicating your concerns to her and she ignored them. I honestly couldn't tell you what would cause such a change unless she was hiding an underlying Borderline Personality Disorder at the beginning of your relationship. You offered to find a counselor, which could have made her feel defensive.

I guess the thing to ask is does she understand that this is emotional blackmail? There is a book on the subject and one of the first examples is threatening to kill yourself if your partner leaves. It is used because they know you care too much about ANY person to purposefully act in a way that would cause them to hurt themselves. She likely feels like she has no control over the situation and is desperate to find some way, any way to regain whatever control she had over her life. It's so intense that she isn't even thinking about how she's affecting you. She's not even thinking in terms of like, ok, worse case scenario, you do leave... Then what? She's single for a while and gets to have the apartment/house to herself. Big deal?

You need to confront her about these threats, call it out as being emotional blackmail and abusive. I would also tell her that you understand that she's feeling insecure, but that those feelings turned into a pattern of abuse. I hate ultimatums, but I think it's appropriate in this case. She sees a therapist (or you even see one together) or you need to leave for your own health and safety. I'm sure you'd hate to have to end the relationship, but she has painted you into a corner by resorting to abusive tactics. Don't call her any names, don't raise your voice. If she starts arguing with you, tell her you're going to take a walk or drive and will wait for her answer.

I recommend his because if you don't make it clear that it's HER decision to end the relationship (by refusing to see a therapist with or without you), then I'm worried that this could escalate to her actually hurting herself or even stalking you. You really do need to put this on her so that if you walk away, she at least knows that she DID have control over whether you left or stayed.

It's really tough, but I think you'll find some kind of resolution one way or another.