Partner with depression

Hi,

I'm new to the site, and have never posted on anything like this before - I'm not sure if this is the right space - but i need help -

My fiance and i have ben together for 5 years, and she has battled with self diagnosed anxiety/depression during this time (family history of depression) - she's the life of the party to everybody but behind closed doors she doesnt adapt well to change and has suffered traumatic events over the past few years and this has resulted in the past in her falling into very low times - during these times, she has always turned to me, she has always leaned on me and let me in and together we have come out the other side. This past year though she has completely blocked me out, to point that she broke up with me, she said she was too messed up in the head and thought i didn't love her anymore, that she felt worthless and she didn't make me happy. I didn't see this coming but i tried to be supportive, we have since reconciled - but our relationship is strained, we live together and we don't romantically see anyone else but that's where our 'relationship' feels like it begins and ends. She says she feels guily for how she treated me constantly and that she doesn't make me happy - that shes still messed up in the head and toxic. She made new friends while this was all happening and says she like spending all her time with them because then she doesnt have to think about what she is really feeling but when she is with me, i am just a constant reminder of her depression and how horrible she is. I try to be supportive, I try to reassure her i'm here for her and i'm not dwelling on the past but I'm at the point where I don't know what to do anymore, this is the girl i thought i would be spending my life with, my best friend - and yet my pressence seems to just bring her down. She says she knows she needs to get help, but she doesnt do anything about it.. I know i can't fix her.. but i don't even know what to do to help her anymore? Do i leave her if i seem to be the cause of her pain? I know i'm not the cause of her depression, but i seem to be all she sees - and it kills me.