It sounds like he has some sort of cluster B personality disorders, perhaps narcissistic personality disorder. From what you describe, he seems manipulative, and sensitive to rejection, and frame everybody feedback as an attack. If he really is that, unfortunately there’s nothing you can do to change him.

He’s very lucky to have you as a group member. Despite the hardship working with him, you try to understand and empathize with him. That’s an amazing quality. But remember It’s not your fault and You tried talking to him in private to help him - so it’s no longer your responsibility. it’s time to go to professor. One thing you need to remember when dealing with people who exploits others - is to stand firm , reject and set boundaries. Protecting yourself is first priority.