My boyfriend flirts with girls.?

well i dont go up to my b.f and tell him i dont like him hangin w/ girls, becus i really dont care. but he's a flirt, and he doesn't know it. hes goin to the mall w/ a bunch of girls from our skool. [8th grad] and they're my friends too. he asked and begged me to cme, but i just dont want to, becus ill be sittin watchin them flirt wit him. i told him to go, so he is. how can i handle seein him w/ girls who flirt with him?