I befriended with a guy on Facebook 1 or 2 months ago.We talk a lot.I shared all my problems with him and he was also a good guy.But from past few days......he just not replying to my chat or replies very late like 10 or 12 minutes later.When I ask him why you replied so late.....he tells me I a very busy.

Why he behaves like that?

look dear, he is acting like a friend. but your expectations are too much.
if you wish to keep him as a friend you need to stop irritating him with frequent msg