fundamental particles that cause attraction like gluons were not thought to exist and attract the nuclei of atoms together, and yet they do.
How do they tell the particles in the nuclei which direction to accelerate?
The force is observed. In the celestial bodies close to us, gravity works to a VERY accurate degree. Of course you discredit this because of things observed VERY far, which are hard to measure as accurately as the objects close to us (that is, we would expect a large amount of error)
If the fundamental particle theory IS right about gravity in the RE theory, it may very well explain the existance, or lack of, dark matter. Similar to how you have VERY low probabilities of strange occurances between charged particles close up.