Do I stay with my girlfriend or go with her?

Okay. This is a long story, so please hear me out. There's a lot of details and problems that make this problem huge and I sincerely cannot decide.

My ex girlfriend is a very depressed person. She has problems with her thryoid and weight and those arent getting much better so, subsequently, neither is her mental state. When we dated and even for years before I had been her guardian angel. I always made her feel better and could always pull a smile out of her. A year ago, I went through a really hard time in my own life and the weight of her problems were too much on top of my own and we broke up. Shortly after I found another girl who made me really happy, and this is my girlfriend today.

The problem was this was the fact that my ex was never a social person, and after I dated this new girl I left her with nobody there for her. Nobody at our school seems to care about her and her parents never did to begin with. When I left her, I took away one of her only lines of support in life. I won't go into crazy detail but her depression had gotten way worse. So we started talking again. One thing led to another and we're now talking daily and falling back into old habits. With these habits followed romantic actions, and this was the first time in my life I had ever even thought to consider myself a cheater. After talking to her constantly in the latter half of my current relationship, I realized that I still really love her. I noticed that when we talked she got so happy as I've become one of the only people who knows her well enough to get through to her. Needless to say this resulted in a growth of feelings in both directions and I realized how much of a mistake it was to break up with her in the first place.

Her and my current girlfriend hate each other to no end, ive tried to remind each of them that the other is still a person with human feelings. Blind hate isn't worth it because they both have problems and both love me.

That didn't work, and now tensions are higher than they've ever been. It's going to be now or never that I decide where I decide to go with the rest of my life.

Do I stay with my current girlfriend, because I have a lot to lose in this relationship? Do I go with her because she needs me? Is it selfish of me to have talked to my ex in the first place, selfish to assume I'm the only one that couldve helped her?

Is it selfish to keep my ex in love with me while she tortures by the fact that I'm in another relationship My current girlfriend knows I talk to her, but not about our feelings, is it selfish that she has to sit here and watch me text someone that I secretly love?

I'm all out of options. Maybe I'm jaded to the obviously moral answer, and I'm hoping this community will give their two cents.