Best friend not so much friend.?

We've been through so much together, until i introduced him to a couple of my other guy friends. now he is always with them and they smoke pot and stuff all the time. he like never tries to talk to me unless i call him. theyll come over to my house but i think thats cause they know they can get away with anything at my house. all they do is smoke pot. im not going to try to get him to stop obviously because thats unrealistic. i just miss my best friend. it doesnt make sense to me at all. i have a boyfriend, who is really good friends with my best friend. one night me and my boyfriend went out together and my best friend got mad and said we ditched him and is not mad at my boyfriend but is mad at me? like i dont understand why hes doing this? what should i do, or say??