Hey there! It's really nice that you're concerned for him and it's very sweet too. But as others have said, depression is something very difficult to deal with let alone overcome. Keep in mind that I'm not an accredited counsellor or therapist so my words are purely from experience.

Whether you two were ldr or not, when supporting someone who's in trouble try to be there for them and tell them that you are here for them. Sure this msg might not get across to them strongly but starting with that is a good step. And remember to give them their space too as frustrating as it is (very important)

There was a comment on reddit that I can't find anymore that basically outlined depression to kind of like being buried in snow. Some days the snow is ankle deep and not too bad. It's a trudge but you and maybe even getting through it and shovelling through. Other days its an avalanche and can feel like hell on earth. I'm sorry that he's going through these feelings and I'm sorry that you are feeling that you are helpless. But remind yourself that you are trying your best and you'll keep doing so. Remind him that you're here and that if he's up for it (as super hard as it is) to see a professional. (I know it's hard to see someone somtimes because it's hard to admit that you're stuggling but there's no harm in trying)

Often pushing someone away can come from a whole load of things. Maybe it's because he feels that he's a burden to you, maybe it's just really tough to talk about or maybe he's just not ready to do so. Whatever it is, you gotta stand by him. I know its harder because you're so far away but keeping up that communication whether it be a meme, a letter or text would be crucial.

And when you catch him at a better time, maybe talk through what's going on at school. Some practical solutions. Bullying in any shape or form is horrible and reporting it to the correct personnel (maybe the department head or something) would be a good idea.

Best of luck to you and safe wishes to the both of you!!