be there and support him. say that he doesn't have to talk to you about his problems but you'll listen if he does. and try not to judge him - even if they seem simple to you, they aren't to him so try to understand. good luck.
Then give him his space, at times people react badly and they need a break from everyone to kinda collect themselves, when he needs you he will reach out for you, try to stay supportive, but when a person has breakdown it's usually up to them when they get out of the funk.