I feel like this is not your problem or responsibility. It's his life for him to live as he sees fit. So if you want to say anything, you would want to just express your opinion and feeling about it all and not try to "fix" anything about the situation.

So like, you can say you feel concerned about it as you don't think it's an okay treatment of him, but I don't think you can say much more than that. If he talks to you too much about this problem, you can limit the time to listen to it if it feels too much like aimless complaining that just gets you very concerned without being able to do anything about it.