My best friend whom I've known for years is starting to worry me.
When we were at school together he was very active and positive towards life, he was very fun-loving and always had an opinion on something. When we were 14-15 he started becoming negative towards everything, he stopped caring about everything including friendship, we're always taught that this was common for adolescents but recently (we're both adults now) he's been becoming increasingly apathetic.
He constantly puts himself down and comments on the futility of his life, and feigns(?) suicidal thoughts. He's never been the one to seek attention or blow anything out of proportion, but for the past few years he's been gradually falling into a pit of depression, doing nothing but listening to music and playing video games. Whenever I invite him to a social event he just says he has family visiting and spends the rest of the night playing games.
He has a family history of schizophrenia and has an abnormal amount of medical issues, which caused him to have problems with making friends in early life.
I'm becoming genuinely worried for his well-being, what can I do to help him? I feel obligated to help him in any way possible, we've been best friends since high school. I've tried talking to him about his apathy, and at first he would get angry and lash out in denial, but now (past 6 years) he's been open about his feelings, but still refuses to do anything about it.
He studies psychology so he understands what he's going through and how to help himself, but refuses to seek help or create a better outlook on life, he just shrugs and says "This suites me better, I was meant for solitude". Even though he sees himself as worthless and disposable, he still mentions how much our friendship means to him, and that I'm the only person he is willing to trust.
Is there any way I can help him? Or do I have to accept the fact that my friend will drift through his life in apathetic disposition and depression?