That's how gravity works. The distinction of saying which object is falling towards another is arbitrary, really-- we just consider the more massive object to be fixed in space (which it isn't) and the smaller object to be the one "falling" since it is accelerating at a higher rate towards the larger one, but in reality, both are moving relative to each other. Even satellites orbiting a planet don't really orbit a planet, but rather a point in space between the center of the two objects. How close that point is to the center of the more massive object depends on how much more massive it is. If the two objects are close in size, the point may lie in empty space between the two objects-- Pluto and Charon for instance-- who I hear doesn't make change.