On the brink of breaking up, I stay with her, she keeps coming back to me with her problems.

I've been in a long distance relationship since June 29th, 2014. I am still in it, its complicated though. I don't even know how it can end anymore.

I met her online in late Spring of 2014, around May and June, I met her because she knew one of my friends. She was actually in a relationship with one of my friends, then that friend was saying things about her behind her back, so I told her about it. She broke up with him, and I tried to help her through the breakup, at the time, she was also getting verbally and physically abused by her family. We became friends and helped each other with each other's problems, and got to know each other, and about each other's lives. Soon after that, we became best friends and started doing lots of things together, calling eachother everyday, and all around spending everyday with each other. Soon, we got in a relationship with eachother, and got very close, heck, we almost forgout about our lives because we were spending so much time together. It meant allot to me, and she was what made me happy, and not depressed.

That all changed in Fall 2014, I had to leave for about a week to go on holiday, when I got back and we started spending time with each other again, she claimed that I had changed. She was right.
After that, and as school started, I began going into a deep depression, as summer went into fall, and fall went into winter. Over that long period of time that I was in depression, we grew more apart from each other. We went from talking together everyday to not even actually talking for days, sometimes even weeks. I was too depressed and scared to do anything, yet enough talk to her. But when we did talk it was great, and I wasn't depressed, and we talked about how our lives have been going, and we again helped each other, but it was shortlived, and died out, to iterate and reiterate later on in the relationship.

As 2015 started, my depression was still with me, and she was too fortunately, trying to help me but unfortunately our relationship was getting better and worst from time to time. We started talking to each other again but sometimes my depression would come back and we would not talk to each other for days to weeks, and only call each other once or twice every month.

It was in Spring to Summer, that she told me that over a long period of time that we had been together, that she had been lieing to me, and that she has been seeing other people, and has been cheating on me. The person that had been making my days, making me happy the most I had been in my entire life, the best person in my life, the one that was there for me, and understood me, and helped me through all that I had become, had done this to me. It hurt, but I stayed with her because I loved her and care about her, and she stayed with me too because she has problems in her life, and I'm the only person she has for that.
But as time continued, she did it again, lied again, cheated again as I found out more and more of the multiple things she has done behind my back. I still stayed with her, and I'm still with her right now, but we've been breaking apart for months, as its been a year since we've been together. She leaves, and then she keeps coming back with her problems, staying and leaving, and somewhat forcing me to be with her and help her, I don't know how to say No, because I care too much about her still, and I'm afaid if I don't help her then that something dramatic will happen, because she is just as mentally ill as I am. She has been abused, and depressed, and has said multiple times to me that she was tempted to commit suicide, but she again keeps leaving and coming back. Of course I keep staying with her through all this, she is still the person that I have feelings for and love, even though she has lied to me and cheated on me countless times, I still love her and care about her and want to have love if we can. But it feels like it will never end, and never get better for and between the two of us. We both are hesitant to break up, and move on with our lives, but we keep having feelings for eachother that change as life goes on, and we don't know what to do, more importantly I don't know what to do, after all this. I know its not love, but what are me and her going to do? I simply just don't know anymore at all.