When he cries hug him, he will know you love him and it will help him release it. Just by being next to him or near him without saying anything helps, just knowing that there is someone there for him if he needs it. Try to get him something that he likes kind of like a surprise, it will put a smile on his face and let him know that its alright to smile even though he has lost someone that meant so much to him. If he wants to talk about it or anything, talk to him and if he doesn't just be there and let him know that you are there for him I hope this helps