It is easy for a caring person like you to get caught up in a spiral with someone like this. It is good that you care about what happens to her, but folks here are right - You can not let her keep pulling you in to her unhealthy life.

It is NOT your fault that she is mentally ill, nor that she is in the hospital. Her telling you that is it is your fault is emotional abuse, as were here comments about your music, her intereference with your talking to other girls, her nonsense with hugs/phone calls/sex with other guys.

This girl's Bipolar Disorder is currently out of control. Until she is stabilized on medication and has had a decent amount of therapy, she will be unable to have a healthy relationship (friend or otherwise) with anyone, and it will do her more harm than good to try. She cannot handle it. It makes her be bad to you, and bad to herself.

If/when she calls you or approaches you in person, simply say something like:

"I care about what happens to you, but you and I cannot have a relationship like we used to have. You need to focus on getting yourself well. When you are in a better place, I can be a friend to you, but nothing more. Until then, we need to keep our distance."

She'll likely keep trying... Then just say:

"<insert name>, get yourself well."

...and hang up, walk away, ignore her, whatever. Say it every time, and say nothing else. If you respond to her tears, her anger, her pleading, etc. in any way, you are giving her attention which will just encourage her bad behavior.

If she gets herself stabilized, it will be very clear to you in her new approach to you, and she will probably tell you the status of her meds, therapy, etc. to let you know that she is working on herself. Then you can be supportive of her, and try building a friendship (ONLY) with her if you wish - but be prepared for setbacks, and revert to your one line response if she gets off the path to mental health.

Remember - Guilt is like a bag of bricks; all you have to do is put it down. None of this is your fault or responsibility. Don't let yourself buy into that.

If you're having trouble letting go, remind yourself that it will not be helpful to her for you to be around her while she's out of control. If you have to, put a rubber band around your wrist, and whenever you feel yourself caving in to her antics or feeling guilty, give it a good SNAP. Train your brain not to fall into that trap. Your emotional health is at stake!

Best wishes.