This is a misunderstanding of what "theory" means. Theories in science aren't "just theories". They're specific explanations of natural phenomena. There is no pathway in science for a theory to progress into a "fact", because that's just not what the term means. A fact is something that has specifically been observed, zero inference. It is a fact that this apple I dropped fell to the ground. It is a fact that Earth orbits the sun. It is a fact that the solar system orbits the centre of the Milky Way galaxy.

"Gravity", in itself, is not a theory. It's the name given to the observed phenomenon of objects attracting relative to their mass. A phenomenon that has been described by Newton's Law of Gravity, which tells us that the force of gravity is proportional to the M1M2/r^2^ where M1 and M2 are the masses of the two objects (e.g. the Earth and my apple) and r is the distance between them. Newton's Law proves useful at small scales, but fails to explain some phenomena, which is why Newton's theory of gravitation, while it was extremely useful in its day, has since been replaced by the explanation of gravity within Einstein's general theory of relativity. A good theory should be testable, and a great way to test a theory is to predict something hitherto unobserved. General relativity predicted gravity could bend light even though light is massless and thus would not experience gravity under Newton's theory. This was confirmed during a solar eclipse just a few years after Einstein published the theory. And more recently scientists measures gravitational waves, another Einsteinian prediction.

But even Einstein's theory of relativity does not fully explain all observed gravitational behaviour. Many large galaxies rotate at speeds faster than would be expected based on their observed mass. This phenomenon has been named "dark matter". Multiple theories exist to try to explain dark matter. Some say it's a specific type of particle. Others say that gravity is wrong and should be modified. Dark matter is an evolving field of research where, unlike relativity, no one specific theory is yet accepted by the vast majority of researchers.

TL;DR: gravity is the name given to the observed phenomenon of objects attracting. Multiple theories of gravity have existed as more evidence is gathered. Today, Einstein's general theory of relativity is held as the best. But dark matter (a phenomenon) puts a spanner in the works of our understanding of gravity. There are multiple different theories to explain the phenomenon of dark matter, none is universally held.