Hmmm.....lost 50lbs in 3 months just by dieting? Are you sure he didn't take diet pills or any other street drugs to accomplish that? That's a lot of weight to loose in a fairly short period of time. Just a thought.

Depression.....has your friend ever suffered from depression? This could be something to consider. How about major changes in his life (aside from weight loss). Family issues, money issues, has he moved recently? Anything that could be causing him some stress and anxiety might be playing into his moods and comments.

I would be asking questions....as a concerned friend and of course validating how he's feeling. Maybe he's scared of something and he doesn't know how to discuss it or how to bring the subject up?

It's hard to say exactly what could be causing his issues. I hope he is feeling better and back to himself soon. I'm sure you will be a good friend to him.

Take care!
_sabby_