Coughing up blood is not a good sign. I would suggest you convince him to make an appointment to see his doctor right away. This could indicate tuberculosis which is highly contagious and serious. Regardless, he could also talk to his doctor about the problems he's been having, back aches, etc, and hopefully receive some help. I know it must be hard to watch someone stuck in a habbit that's harming them, like smoking, but unfortunately everyone but he is powerless over changeing him. All you can do is provide resources and be there for him when he is ready to quit
Make him go to the doctor! We aren't qualified to make a diagnosis let alone guess. He must see a physician!
Good luck!
p.s.
He should quit smoking that would be a great start!