EEEEK, this is a hard one....
Can you find out more about this tumor? I lost my mom almost two years ago to lung cancer.
If I were you, I would try to find out more about his condition, maybe it isn't as bad as he thinks it is, he is so young. I am sure he is afraid and even your friendship would be a great support to him. Is it possible for you to talk with his mom without him?
We are all being watched.... StrawberryFields