Hi, Mike. Your story is interesting. Most of pupils often see such things as you described and I am one of them.
I think that you should try to talk to your friend about this problem. Try to explain him that if he continues cheating, he won't pass the exams. It must help him to choose his own way ov living. If it doesn't help, then it's not your fault, it's not your life. The most important for you now is not to repeat his mistakes. Take care of yourself, bye.