If I just wasn't born, my mother and father would never have stayed together.
I would never have ruined so many peoples lives by myself.
I'd no longer be a burden on my mother. The bills would get easier to pay without me being such a leech.
R could be with S and she'd be sad but she'd get over it.

I've had one sweet bit of logic to fight back with:
Existence harms. Nonexistence harms worse. That won't be my problem after this.

I still have people who love me, including my mother and R, and that's what matters. As long as they're there, I have purpose, I have meaning, even when I don't think I do, and I need to grasp onto that with all of my power.