Like others have said, you need to talk to him. Sometimes, people just can't be available for a relationship because they have too much going on in their lives; whether it's work, school, or other priorities, it's just simply not possible to extend your energy beyond what you have. The partners of those people end up suffering for it, but why should you? You need to be a priority, too. You're a human with needs, and if he can't meet them, then why put yourself through the grief? Breaking up with someone you love and care about is incredibly difficult, but sometimes, it's the only way you'll ever be happy in the long run.
But before you think about all of that, talk to him. Good, healthy relationships are based on good communication. Tell him that you're lonely and you don't know if you can take it anymore, and stick to your guns about what you want and expect from him as your partner. He may not realize how you feel, or how fed up you are. Best of luck.