So if you have a bff right, who loves u and u love him.. but some other guy comes in should i fell threatened?

my bff and i are extremely close and im felling threatened because this guy... we really dont like him like he thinks we do... and he keeps acting like hes his bff when hes not i am... but im getting so angry or even jelouse if you can say... but should i be thouguh? im kinda lost now lol because i really wana hurt this guy... HELP.. lol