Hey there, I know it must be hard to accept and it is good that your caring for him, but there is not alot you, yourself can personally do for him. All you can do is when he is depressed is for you to talk things through and comfort him this might make him feel a little better. I know it seems like the end of the world to begin with when someone dumps you but explain to him that things will get better and easier as time goes on. I know it seems like it wont but it will.
If he is really feeling bad about himself maybe he should tell his parents because ultimately he is their flesh and blood and I'm sure they will care regardless of what he might have done in the past. Talking about things is one of the best ways for things to get better otherwise the problems just carry on and build up to a point where it gets even worse. Maybe he could could get referred to a counsellor because every thing said there is confidently, so he would not have to worry about that. I know it is scary for him, but if he gets better then it is worth it, right?
If he intent on not telling anyone, do you have a number for his parents and give them a quick call? I think they should know. I think where is under the age, i think the school has the duty to contact the parents, but the best way would be for him, to tell his parents himself. Maybe is one of those people who do not like to confide in people especially parents because you never know how they are going to react, but regardless im sure they would appreciate being told because after all im sure they would just be worried about him.
I hope i have helped, Good luck!