These topics are always hard to deal with. The fact that he understands that the way he is living isnt healthy is a good sign. Nobody WANTS to be a bum. I think that therapy and medication would be a HUGE benefit to him. I am 24 years old and when I was his age, I went through a period of being lazy without a job and living with my parents. I was later perscribed Wellbutrin and Adderall; now I have my stuff together. Medication helped get me off of the couch so maybe you could ask him to make an appointment with his general doctor. Give that a try before you leave him.

You seem like an amazing person. Mature and responsible for your age with a bright future ahead of you. Trust me when I say, he knows that he is lucky to have you in his life.... But you can only help him so much before you eventually will need to think of YOURSELF and whats best for you. Try medication and therapy (if you can afford it). See if that helps. I wish you both all the best! Keep thinking positive!