Why don’t some women understand allowing men to flirt with them while they in a relationship could cause a lot of issues?

Anonymous
So I notice that girls I’ve dated and a few of my close girl friends all think it’s okay to allow other men to flirt with them even if they have a boyfriends. Almost all of them pretty much said will my boyfriend should truest that I wouldn’t sleep with a guy friend just because he hits on me 247 it’s no big deal. I don't know if this is just because of we’re I live but even when I dated someone and we have zero issues they all always have that one by guy friend they allow to flirt with with them , my girlfriend won’t ever flirt back. Sooner are later deal with this wears me down we have a big flirt and that guy friend turns into someone they start flirting with. Maybe I’m doing something wrong I don't know I’m good at sex , I have a big dick, I’m a romantic boyfriend. I do something forget to flirt with my gfs to get sex or make them chase me etc
Why don’t some women understand allowing men to flirt with them while they in a relationship could cause a lot of issues?
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