How I know that my girlfriend sex with another boy?

i want to know that its possible to know that my girlfriend sex with another boy or:i want to know that it's possible to know that my girlfriend sex w

i want to know that it's possible to know that my girlfriend sex with another boy

or:i want to know that it's possible to know that my girlfriend sex with another boy

or:ask her to have sex, then you will know...

Tags:sex,