You are absolutely right. Your boyfriend isn’t holding you close through love, he’s holding you hostage. He knows it would be hard for you to live with yourself if you broke up with him and he hurt himself. It’s unfair. It’s not at all what love is about.
I think you are also right that you can’t carry him any more. It’s time to call in reinforcements. If his parents are decent people, arrange to have a talk with them. They have a right to know that he is in this much trouble. They are in a position to insist that he get help. If you don’t think his parents are a good bet, then please talk to your school counselor or nurse or to a favorite teacher.
Please don’t worry about “betraying” him by calling in some help. Some secrets shouldn’t be kept. Even therapists are released from the rules of confidentiality when someone is threatening or practicing suicide. Our first job is to keep someone alive.
Turn this fellow’s care over to someone who has the resources to actually be helpful. Then break off the relationship and take some time to recover. You might want to see a therapist yourself to help you learn from this experience and to help you deal with any guilt and anger you may be feeling.
I wish you well.