Those two objects are ALWAYS in each other's gravitational
field. And gravitational forces always appear in equal and
opposite pairs.
When a small object is released in a position near a more
massive object, both objects move toward each other, with
increasing speed.
There's a gravitational force on each object, attracting it
and drawing it toward the other one. The force on the
small object causes it to accelerate toward the more
massive one. The force on the more massive object
causes it to accelerate toward the smaller one.
The forces are equal. But since acceleration is inversely
proportional to mass, the small object heads toward the
more massive one with greater acceleration, and the more
massive object heads toward the smaller one with smaller
acceleration.
When you jump into the pool from the high diving board,
you accelerate toward the Earth, and the Earth accelerates
toward you. The gravitational forces between you and the
Earth are equal in both directions. But the Earth has more
mass than you have, so its acceleration toward you is smaller
than your acceleration toward it.
