I can see why someone would choose to live with their partner or not to.
I recently took the leap with my boyfriend and I was the one who had anxieties. Not that we would break up or anything, but still... what if? How would we split rent or deal with awkwardness. I was comfortable and confident in my relationship, but on the other hand I didn't want to be naive.
I let him know my anxieties weren't personal, and we talked about it. And I'm quite happy with the arrangement.
It really depends on the couple, everyone is different.