I'd tell him nothing. I would tell his girlfriend though! He knows what he's doing. And he's not giving her the chance to make an informed decision. He's a dick. She deserves to know.

People who love each other don't act like that. You're codependent. Not in love.

While you both didn't choose the mental health issues you have, you are responsible for how you act and what you do to help yourself. You admitted you're not in therapy? Why?

Are you an abuser? Yes. You hit someone. And you threatened to kill yourself to make her stay. You need inpatient care to stabilize and deal with these issues. She cannot be your therapist.

Right now in your current states, you two should not be together.