Completely understandable. Why wouldn't it? I can tell that your friend meant the world to you and I can sympathize with such love. Having someone who understands you and accepts you no matter what is one of the most comfortable relationships to have... The loss of which is like a vacuum where happiness ought to be. It just feels wrong. Your dedication to respect his memory is very admirable.
Almost all my work in some way comes back to him, though.
I wish I could give a cure-all for grief, but there isn't one. It's a life-long process. I am sure you know that already. If depression makes it so you can't create (and I don't say that to be rude or presumptive, I say that because I have been in that situation), then another coping mechanism I can relate to you is that I will seek comfort in animals. Dogs are the best animals. They don't judge. They just want pets and snacks and they will love you unconditionally. They are sponges for pain. I'm in university, so I can't have animals. Though, I occasionally do volunteer at the animal shelter when I have the extra time giving rescued dogs walks and such. I also hijack my friend's pets and spoil them rotten.
If all else fails, I travel. Not even that far because, like I said, university. Walking and exercise releases endorphins and it feels good. When I walk, I visible make progress. Like creating something, it's a tangible and it's easy to wrap my head around. It's the little victories that help in the end.
I'm not going to give you direct advice because I don't know the details of your situation, I don't know you, and I would be a pretentious ass to assume I can solve all of your problems, no matter how much I would like to be able to. I will say, however, that I also made the switch from art major to english major due to emotional distress, though our situations are different, so I do feel for you. I also swore off art for a time but I came back to it eventually when I got my barrings again. Anti-depressants can be a worthwhile crutch and one that I certainly used for a time just so I could make it through everyday routines that others take for granted. Therapy, while it does not work for everyone, can be beneficial to some people just as it was for me. I'm not telling you to seek them out, just that they are good options despite the severe stigma attached to them.
Regardless of all of my rambling, please keep yourself healthy. Keep eating. Drink fluids. Get some sleep. That's what matters most.