Gravity appears to act as a force so it would seem natural that it is bi-polar. However, as jpetruccelli says, GR means that spacetime is curved. Elaborating on that a little bit, the presence of matter distorts the spacetime within which that matter exists. Gravity then, instead of being a force that acts on matter and creates the distortion, is actually just another way of describing the the distortion itself.

If I'm allowed to misquote you :) just because space is skewed, there is a force.

I'm a bit rusty on this bit and may be remembering incorrectly but because there are no universal reference points in spacetime any distortion of that spacetime is neither positive or negative and so can't be bi-polar. It also might help if you think about how the mass which creates the gravity/curve in spacetime in the first place is uni-polar in nature too - we don't observe negative mass anywhere - even if we can hypothesize about it's behaviour.

In fact, because we have local reference points, we can view the force gravity as bi-polar. but only in relative terms. From the bottom of a gravity well the direction is up but from the top of the well it is down.