The Strong Force is responsible for the binding of nuclei. This force is so strong that it binds and stabilizes the protons of similar charges within a nucleus.
The Gravitational Force exists wherever there is matter. This means that the larger the body, the stronger the force. But on the scale of individual particles, the force is extremely small, only in the order of 10-38 times that of the strong force.
In a nutshell, the force holding an atom together is stronger than the force that's trying (and failing) to hold the universe together, since every galaxy is flying away from every other galaxy at ever-increasing velocity...notwithstanding our eventual collision with Andromeda, which, if we're lucky, will occur before the rent comes due.