If two opposite charges get farther apart, does their attraction for each other increase, decrease, or remain the same?

The force between them decreases, as the square of the distance.

For example ...

- - If you move them apart to double the original distance, the force becomes (1/2²) = 1/4 of the original force.

- - If you move them apart to 3 times the original distance, the force becomes (1/3²) = 1/9 of the original force.

- - If you move them apart to 5 times the original distance, the force becomes (1/5²) = 1/25 of the original force.

(Gravity works exactly the same way.)