Unobvious disorders/problems?

My friend has a problem and he won't tell me what it is. He says there's only one medication for treating this particular problem, but the medication only alleviates some of the stress ociated with it. It's possible that while struggling with this problem, one can make mistakes that can cause them to die, or struggle with it to the point where they kill themselves. It's not outwardly obvious to people around him, and he claims it will never go away. It's a psychological problem that can end up as a physical problem and lead to death. It's also the reason he won't be in a relationship with me. It can be hereditary, and sometimes it can be caused by a certain event in a person's life.