If a person does not want to parent, you can't make them.
If a person parents different than you, it doesn't make the other person a bad parent.
Instead of worrying yourself sick over this, you could take the proactive step, start filing for custody now. Speak with an attorney, figure out what YOU need to do. Right now, you are letting him control you. You should be in control of yourself. You've got at least 16 more years (maybe even more) of dealing with this person, better start figuring it out right now.
What I would do in that instance is call the local cops/firemen and report his threat of self-harm. Ask them to do a check on him. If he says anything to them about feeling suicidal, they'll take him to the hospital for an exam, and the help begins.
I don't advise you to take him yourself, in case he is violent toward you in the car. I'd leave it to the professionals.