Why would matter have an intrinsic need to coalesce with itself?

According to Relativity, anything with mass creates a curvature in the space-time continuum. It is this curvature that causes matter to coalesce, not matter itself. Also, when enough matter come together, it is the pressure from the gravitational collapse that causes fusion to start, again not matter itself. Matter cannot go back to the state of energy by itself. The 2nd law of thermodynamics gave a very specific direction, ie entropy (the amount of useless energy) must increase. The ultimate state of useless energy is actually matter itself, specifically iron. If the Universe continue to expand forever, eventually it will exhaust all useful energy and everything will be just matter.