You can get an idea of how your girlfriend will treat you later by watching how she behaves towards her little brother.
I'm reminded of that sometimes with children. I think we need to generally treat children with more respect and politeness.
For example I was at a place today, and two little children came in. They were smiling, happy, well-behaved. But if you listened to the way the adults spoke to them... "Do this!", "don't do that!", "go there!", "don't go there!"
Any adult who were spoken to that way would be quite insulted, certainly I would.
We speak to children that way for a very simple reason: because we can. Children are small and dependent on adults, they have no power.
I once saw a mother and her girl, perhaps 8 years old. The girl was crying and did not want to go where ever they were going. She was earnestly crying, she *really*, strongly, did not want to go. The mother didn't care, she said "well, we go this week, maybe we won't go next week". The girl said "you also said that last week. And next week we'll just be going anyway too..."
It just broke my heart. It was clearly an optional thing they were going to. And it would have taken a *very* important reason for myself to force somebody to go somewhere they clearly felt so deeply about not going to. That girl was in pain about it.
[Granted, there could be data which might make me see it differently, but I find it hard to imagine.]