There are theories out there that answer your question. You just have to look for them.

My spin (whether it is pulled from a memory of a fragment of a theory), is that everything in existence is based off of cycles. This is how the singularity came to be and will be once more. I think a theory states that if there is a limit to the spacetime expansion, then space itself will reverse and collapse under its own "gravity."

To me, I see the universe to be like our sun. It will start to die and expand as a red giant until its mass is completely unstable. Then at some point it will go supernova, loosing all of its mass, creating a blackhole (a metaphoric singularity).

To me, if the Big Bang Theory is right, the Universe as a whole has its own gravitational center that will bring all the energy and mass back to the center. If another theory is right, we may just expand into eternity, but I personally don't believe that. I believe in cycles.