We really donít know what causes gravity ( mass properties ) only how it works in the present universe state.
There has been a philosophical debate for a long time as to weather mass gets its properties from the rest of the universe or if it is an intrinsic property of mass regardless of the state of the rest of the universe.
On the part of the individuals who think that the properties of mass are intrinsic they may point out that currently accepted physical mathematics assume that the properties of mass are intrinsic and provide correct physical predictions.
The individuals who think that the properties of mass are due to the existence of the universe would point out that if only one mass existed you would have nothing to have a velocity, acceleration or attraction force with respect to and mass properties would not exist.
You assumed that gravity existed without the universe in its present form..
and have reached the logical conclusion the the universe can not exist....
but it does exist.
It may be that you have just proven your assumption is wrong and gravity/mass properties do depend on the present universe state to exist.
If gravity did not exist due to the state of the berthing universe then there is no expectation that the universe would not continue to expand.
This of course leads to an interesting conclusion.
If gravity started from zero and is continually increasing as the universe ages, then the universe may be closed.
Even thought at present gravity strength, the universe would not be drawn into itself again, a future increased gravity strength may cause a collapse of all matter.
Somehow the thought of a closed universe has always been more mentally pleasing to me.