My boyfriend takes drug on occasion should i stay with hims?

ok well only known him for 5 months in that time he says hes took coke once.......hes told me he used to take it nearly every weekend when he was younger but doesnt do that anymore....he hardly goes out anywhere and does stay in a lot doesnt drink a lot either......says hes dabbled with pills and other things in tha past also but because of his diabetes the doctor said certain pills could kill him........i no his best friend is always doing coke still aswell and hes a bit of an idiot tbh and think he has a big influence on my boyfriend......what im really worried about is this weekend he is going away to a festival and yes i put two and two together festiivals most people are out there face.......so on msn he said u wont miss me cause ull be out drinking all weekend....i wrote back well youll be too busy snorting crap up your noise too miss mes.....he wrote back my friends have asked me loads of times what pills and stuff i want and i said i dont want any.....that stuff kills me man im gonna try my best?????? try my best???? i mean if could kill him??? i no obv his mates will be pressuring him and he prob wills.....i dont no what to do im kind of anti drugs as ive had bad experiences in past what do i say to him or do?