There is no such QUANTUM as a GRAVITY; why?

Because there is no such TON as a GRAVITON.

What actually "exists"? 

A bottomless gravitational HOLE in the fabric of space-time, demonstrably bearing an apparently non-finite radius of ZERO, i.e., both of the nuclear forces are gravitational.

Understanding this will be impossible for anybody trained since childhood to become rotationally-challenged. First, we need to correct for this abysmal math's teaching. If one had wanted to study electrical engineering, then one would have had no choice, these engineers have to be taught by highly specialized Gaussian School applied mathematicians. We actually live in an electrical Universe. I know that it is nice to think of having a mechanical body, but actually our bodies and our environment are quantum-electrical.