how can something infinitely exist?

if you draw a number line (actually that's invisible because a line has width and depth (height) ) it can go on forever. it goes forever to the left. and it goes forever to the right. or any direction that's 180.

anyhow, if the universe can go further and further. how do you know where the universe ends? you say, it doesn't end. but if it doesn't end how can it exist. you have an infinite existing real estate here.