Dealing with my ex's depression?! Please help

Hey, this isnt a case of I dumped her, she's depressed etc, its completely the opposite.

The story is, is that she split up with me. Yeah I hated it and yeah in a way i still do. The thing though that is bothering me the most, is that she told me after the breakup that she suffers from depression, depression she's had since she was twelve years old. She is now nineteen.

So its been two months on after the break-up and we have indeed still kept in touch, we have stayed good friends and most of the time get along (we have had a few arguments). But now I feel I have myself stuck in a major hole I cant get out of.

She cant handle her uni work, she is falling out with her friends, she is crying all the time and she is always snappy with me (more than anyone else i might add).

I try my hardest, and when I mean try my hardest, I mean it. I am always there for her so she can cry on my shoulder, I still help her out with all the things she cant do, i help her with all her uni work. I shower her with my comfort and compliments. All in all, i am still like the boyfriend she split up with. I have always been there for her since the day i met her, and i still am. But she is just not happy. She even admitted it herself that I am the only one person she can always rely on but I try my goddamn best but nothing ever works.

I feel I am stuck in a hole, I want to help her so much but its even getting me down she is in this state. I am on the verge on giving up on her entirely. I know it sounds absolutely horrible but its how I feel. Yeah i still feel for her majorly but I can't deal with all the guilt trips she puts on me, I won't name them but she plays all the cards on me, bad ones, real bad ones that make me feel like a horrible, rotten person. And when I even try to tell her about one of my problems, I don't recieve the same treatment I give her. I feel so taking for granted right now.

There are times, I dont want to contact her ever again but I honestly could not live with the guilt of it. I promised her that I'd always be there for her to help her through all her problems. In a way it feels like she justified our breakup with her depression. I feel cheated ina way.

She is a lovely amazing girl but is majorly troubled and now I find it hard to deal with her. Like i said, I cant handle her guilt trips on me and I cant handle her snapping at me. I want more than anything than be friends with her but right now I am on the verge of calling it a day altogeather with our friendship.

Please, could someone offer me any advice in how to approach it?

Will be much appreciated

(I know depression is a serious thing and I dont want to sound insensitive about it, please forgive me if any of you find my post offending)