<human>: Could you distill the essence of the text into 1-3 sentences?

I have severe major depression as well as Schizoaffective disorder. While it is not an excuse, I was very lonely for a long time and started dating A [15/F] on December 1, 2014. Now, she is also severely depressed and has told me many times that she would probably kill herself if I break up with her. She lives in Michigan and I live in Utah, though. The relationship was very real and got quite intimate. This past July I started losing interest in her romantically, but she is my best friend and I don't want her to kill herself or hurt herself because of me. My second girlfriend, the one I am interested in romantically is the same age as me, [16/f] and makes me feel better about myself. She has soothed me during bad episodes of my paranoia as well as talked to me when I hear voices. She is very compassionate and I like her a lot. I want to be with her and I want to continue my relationship with her, but I don't know how to break up with the other one without her killing herself. I don't want to be a cheater, but I don't want her blood on my hands. How do I 1. Tell the second about it and 2. Break up with the first? Sorry for any errors I may have made typing this, English is my second language.
<bot>: First girl is depressed, said she will kill herself if I break up with her, I actually like the second girl and want to end it with the first.