Is this just me, or do i know the wrong girls?

im 15 going into grade 10 and i have a girlfriend(she goes to a different school) who is also 15 going into grade 10 i trust her completely but it sometimes makes it hard because everygirl i have basically known somewhat cheats on her bf like every girl i know from my school will flirt with other guys tell them there hott sometimes say it to me but i ignore it and theyll let guys be close with them like in pictures ive seen girls where there just kissing other guys on the cheeck and they have a bf so do i know the wrong girls? or is this just me because my girl doesnt do that and i love her