I get really jeleous and over protective of my boyfriend...?

weve been dating for about 6 months, and everythings good but we argue alot because i get jeleous of him seeing/talking to other girls. Theres about 3 girls, that he texts alot, and spends alot of time with. They say hes there best mate, but he always tells me he doesnt like them that much. When there together though, there really close. And they flirt. When i get jeleous, we always have a argument. Any ideas what to do?