You're thinking too three dimensionally, which is understandable given that we only experience three dimensions directly, the problem can still be somewhat understood on an intuitive 3D scale though- here goes.

Imagine a balloon with nothing outside of it... Really nothing, not emptiness or space, just nothing. If we draw points on its surface then inflate the balloon the points will travel away from each other in equal measure. Everything outside the balloon is still nothing, and everything that exists is still balloon. If you shrank yourself down to stand on one of the dots the surface of the balloon would appear to be two dimensional, you would have no perception of the third dimension where the balloon is growing. Everything is 2D balloon, and appears to expand as the dots spread away from each other.

We are in 3D, we can't see any further dimensions, but those are the directions the universe expands... Not in, not around, but "through" our three dimensions. Everything is the universe, everything else is the universe, travel long enough in one direction and you end up where you started because there is no edge for us and anything that isn't Universe is simply nothing.

We're expanding into nothing. When asked where it's going it says, "nowhere." When asked what it's doing it says, "nothing." Nothing's a lot of work. You can do nothing all day and still have tons of nothing left to do.

The thinking, as I understand it, is that space curves upon itself in a way that looks linear from a subjective perspective, so you could go straight forever and eventually arrive at your starting point. Space and time as we know it exist only within this growing bubble, so there's no edge to the universe, and no before (or after) the universe. That doesn't mean that other physics don't exist outside of our universe, but that we are confined to our universe and currently have no way to observe or measure outside of our bubble. What makes this concept so difficult is that we have nothing analogous to compare it to; we think of bubbles, balls, and balloons, but those objects aren't especially similar to this universal model. We lack an intuitive sense about how things work at very large and very small scales, so the idea of a confined infinity at the largest scales doesn't make intuitive sense to us any more than the idea of waveforms collapsing when measured at the smallest scales does.

That’s an assumption that’s not necessarily correct. And just what constitutes nothingness?

"out there"

I don't know but it is fun to think about