New person now my mates are boren??

hi im 14 and i just started a new skool and i got to see all my old mates which ive known for years and years but the same day another boy started and he is mates with my best old mates now when ever i am with my old mates and they see thi new kid they all go and hang around with him not everone in my gang likes the new kid but i dont like him stealing my mates he is freindly with me and he is kool but im not kool with him geting my mates which ive known for 5-6 yrs and the first day he gets my mates . what can i do???