Let's look at what all that means more closely:

You leave an object with mass m1, "at rest" inside a comoving frame with mass m2.

After an interval of time the two objects are at different positions x1 and x2.

This happens because they "start at rest" in independent orbits - this won't happen if they both are at constant velocity, and moving through a field (of

__only__) G.

If you want to know about the alteration of positions over time, you need a discrete or continuous time derivative of change in position over change in time dx1/dt1, dx2,/dt2,...

You want a map of velocities v and times t that relates the changes in orbit to g, m1 and m2.

DH said:

When there is zero relative velocity there is zero relative acceleration.

When there is a mass density there is acceleration, of the mass towards its center.

Replace a mass density with a small radius "ball of test particles". If they are in a "box of spacetime" and have a constant velocity they will accelerate toward each other and the radius of the ball will contract. Over time the mass density at the center will increase and the radius will shrink. You are standing on a larger ball, but the effect is the same. over time gravity compresses balls of particles together. Therefore gravity generates density of mass, a singularity of curvature.

So if Einstein is correct, launching a rocket that reaches a constant velocity v > 0 and leaves the singularity behind, its inertia will be due to the fact it has density and is accelerating towards its own center; if its velocity changes it will accelerate "toward G", which is the field.