Hey there, similar situation in my life quite recently. My relationship of 3 years ended and I think my depression and the continuing depression of my ex are to blame.
Two years ago my Grandfather and my Grandmother both died within a year of each other and it hit me pretty hard. They were pretty much my parents and gave me the loving home that a kid needed. We were very close and the loss of both of them hit me incredibly hard, I'd never lost anyone close to me so had no real experience of loss. To my ex's credit she was there for me but did not completely understand as she had never lost anyone close to her.
My ex had depression as well, she seemed to take everything very badly and worried about everything. I tried my best to reassure her but nothing seemed to work and frequently would back fire all together with me the focus of her anger and frustration.
Eventually she actually had something real to deal with in the form of her parents separating. This cause a completely unexpected rebellious streak and a general feeling in her that her life was horrible and that she need to completely change it. She proceed to push me away and push away most of the friends she had made during her time at uni. We were all quickly replaced by ppl she worked with.
Of course the news that I had been replaced by a person that is basically a complete personality clone (all the same hobbies, likes, dislikes and general stuff) basically destroyed me.
Months later I"m feeling better about everything and am now just sad that depression was allowed to destroy our relationship. Just have to put your chin up and live with the knowledge that depression seems to override love and kindness and accept that in certain situations no path is the correct one. Help and love yourself and don't let this bring you down, because all this means that you are a good and caring person to have such a loss affect you so deeply. thats my view point anywho, take care.