[joelr]

In a perfect world one may have no insecurities but usually once you start seeing someone regularly and begin to fall in love both partners get curious about if the other person would still consider dating someone else. If the person met someone whom they felt very attracted to. I think Cylon pretty much said that also.
So "girlfriend" ends up meaning - someone you see exclusively.

It usually does come up especially if the partner is very attractive. Jealously is a tough one to bypass.

Many times it just becomes obvious. She's moved clothes and living stuff to your apartment, sleeps over most nights, months have gone by. Then it's a casual conversation - "So am I your girlfriend...?" half kidding but serious. Or during pillow talk it gets solidified.
One recent GF after 1 month I found myself asking her if she was or wanted to be my GF or something like that. It turned out that it meant a lot to her for me to bring it up.
It's still a somewhat arbitrary label but the fact that she was so happy gave it a meaning.

I was so smitten that it was quite fun asking, it represented a formal version of something abstract I was trying to convey.

I have been purposely dodging the label these days and letting relationships fizzle out.
If I meet someone who I care for as much as that GF I'll probably follow the same pattern.