My girlfriend is a joy but she has depression. She cuts and hurts her self. She seems unhappy but says she is,she says all kinds of the things. I hug her kiss her and always calling her beautiful, wonderful,and amazing. When I say I love you she says it back quick. What can I do?
Seems like you are doing what you can so far - you are there for her, try to make her feel good etc. 
I am sure it is hard for you to see her suffer & hurt herself but you can't solve that problem for her - she needs to do that herself. If she doesn't see a doctor already maybe encourage her to get some help but don't force her. Educating yourself can't hurt either but then ask her what you can do - she will be able to answer that better than strangers on the internet, I would assume. Everyone is different & needs different things after all. Good luck & I hope she gets better.
If you are looking for the input from other people who suffer from depression to get some ideas or insight (which will be very likley more there personal experience though) - maybe posting that question in the depression group on here as well might give you some more answers from people who suffer or suffered too. I only stumbled over your post by accident. I have dealt with depression as long as I can remember - I have it under control but I feel like you should really ask her specifically to really help her...other people can only tell you what would help them, as I said, they are not her. Good luck though.