I went through something similar a couple times I had a crush. It was painful, but I eventually got over it. Both girls let me know they were not interested in me 'that way' and were nice enough. It's just hard to turn off emotions when they reach a certain level... I would just give your friend time and room, he will probably get over it eventually, but people can be something of an energy drain when they are suffering, and can lash out, so be cautious.