One of my closest friend's suffers from depression, or he 'did' and the counsellor said he was fine last year but he doesn't think so and to be honest neither do I.
He takes everything to heart, he ruminates, he get so, so angry over things the people around him haven't even considered, he breaks down and doesn't let anyone see and he finds it hard to tell everything he's feeling because he thinks either no one will care or we'll all think he's a mental case.
I've recently come to bare the brunt of his anger, a few months ago he told me he felt more than friendship towards me and I had to let him down, since then we've been 'sort of' all right, there's always been a slight reluctance for us to get as friendly as we used to but we still tried.
But now he's getting angry at me rather than other people and he often won't tell me why so I don't get the opportunity to apologise or explain myself; I've always been the one he came to if he was upset with anyone else because I was the only one he said he could talk to, but now it's me who has upset him and he has no one else. He said I was the one person he trusted and now he can't trust anyone; I've never felt like the worst creature that ever crawled into existence before. I didn't hurt him intentionally, in fact it all came from a misunderstanding between him and his house mates but even though that had been resolved thing's still aren't good.
I don't know what to do or say to him anymore, I love him dearly as a friend and I want to keep trying, I want to rebuild whatever was taken down and be trusted again but I don't feel like my efforts are working. I don't know what he wants from me, I don't give pity or sympathy to people unless they really deserve it and I try to give it to him but my heart isn't in it when I don't know what's wrong and he can tell, which just makes him angrier.
I'm not strong enough to keep at him when he's pushing me away, it makes me feel like scum that needs to be removed from his life, but I don't think I could cope with losing him as a friend; the very thought sends me into a spiral of panic (I suffer from acute panic attacks and confidence/insecurity issues).
I'm trying to remember things he's said to me about what he wished people would do when he was upset with them; he hates it when they don't know what they've done wrong, he hates 'interventions' and forced conflict, but he doesn't like people pretending nothing has happened either.

I don't know how to make him feel better, he's just gotten worse and worse over the past few months and I know some of the reasons but not all. I hate the thought of him feeling alone and just being left with all this negativity all the time, but I need him to trust me before I can even begin to try and help, and I just don't know how to go about regaining that.

Sorry, but you MUST leave him alone because you can't help, only make it worse. This is something he must do for himself.

You two are feeding off each other and it is NOT GOOD for either of you.
He needs help that is beyond what one friend can do. You may be the most understanding, patient, insightful friend in the world but he isn't capable of getting help out of it. A therapist isn't a magician; he or she has the emotional detachment required.
A deeply depressed person spirals down in a friendship because he both craves and fears your companionship. He knows he's a strain on you, and wants to get you to reject him for your own sake, while wishing you would stay out of the basic need for a friend. "Leave me alone, I'm depressed, and here's all the things wrong in my life, now go away," over and over. There's a lot of selfishness in him: "he hates it when they don't know what they've done wrong, he hates 'interventions' and forced conflict, but he doesn't like people pretending nothing has happened either." That's pretty damn demanding, don't you think? That's all part of his conflict, both demanding and probably hating himself for it. He is totally 100% wrapped up in himself, another sign of his illness.
There's also the very normal problem of one person attracted to the other but it's not reciprocated.

You have to tell him without a lot of explanation that it's time for him to get help because you can't take any more. It's time to put some emphasis on YOU.
I would make a very concrete offer: for every 45 minutes of therapy he has, you will spend 3 hours over the next week with him.