Hello, SnowFlakeUniverse! Welcome to the board!

The attraction does exert a force something like tension in the rubber of a balloon.

Think of it this way:

Pretend the universe is one dimensional (a line) and curved into a circle, and that there are galaxies in this one dimensional universe. Each galaxy is trying to shorten the distance between it and the next universe on the circle, and the only way to do that is to make the universe smaller (or, if it is expanding, slow it's expansion), so GR predicts that gravity should be slowing the rate of acceleration, but that's not what we observe. Actual measurements show that the universe's expansion is speeding up. It's actaually accelerating outward. We don't know what is doing that.