You are asking a lot of very touchy questions in physics in one thread. The question you have asked is a question which several people have tried to answer several times and there are quite a few ideas.
Let me look at your first question, is space infinitely expanding? Spacetime is not going to rip and rupture at a certain point like you may be inclined to believe. The misnomer that spacetime can rip is generated when people used the rubber membrane analogy for the effects of mass on spacetime. Spacetime is infinitely smooth and can be stretched forever and forever without "ripping". This is what Einstein believed. Spacetime can infinitely stretch and never rip.
However, many physicists believed other "sub-theories" which were an extension of spacetime. String theorists who are believers of rolled up dimensions (read about String Theory) believe that spacetime curves around and around like a circle. If you were to navigate in one direction, you would reach back where you are in space. Then there are believers that think spacetime can actually rip when there is a large enough mass (this is the theory of wormholes).
All of these theories are quite difficult to understand and even more difficult to quantify. No one has confirmed any theory for sure because we have no means of confirming anything.
As for your interest in virtual particles. Virtual particles are not particles. They are small ripples in spacetime. Take a look at this link which explains it very well:
https://profmattstrassler.com/artic...ysics-basics/virtual-particles-what-are-they/