[quote=Etcetera]
Do best friends of people normally not trust them with their girlfriend? Like, do people generally worry about that kind of thing?
[/quote]

No. It's just at my school, there are a lot of jerkoffs who think they can win any girl in a pinch. He actually asks me to hang around her if he doesn't trust certain people. I gladly do that since it allows me to get to know more about her and become closer friends.