Throwing up for twelve years?!! Since he was twelve?
He is obviously quite sick. Has he not seen the doctor? Please encourage him to go to his doctor. No one here knows what this could be since many things can cause vomiting. Parasites, infection, vomiting from heavy coughing, internal issues, and who really knows - without a physical examination. He needs to go to the doctor and that is who can diagnose this. If your friend does not have health insurance, he needs to tell the doctor's office before the exam. In this case, they will reduce the exam fee in most cases.
Really - get him to the doctor.