ok guys i need help

ok my best friend mary and my cousin livy r hardcore christians and have been starting a prayer group in the lunch room every breakfast. i love and support both of them and have been constenly telling them how glad i am of everything they do. but my bf doesnt beleive in god and likes to start fightes with them over it. he also yells at them whenever they r praying. he yells things like " all hail santan" and " dont let them drag you down with them." i try to get him to stop but he wont listen. he keeps asking me for a good reason and i tell him becuase its wrong to do that even tho u dont beleive wat they do. 2day at lunch he txted me and said "u need to choose wat u r" he never told me wat he meant by that but i'm pretty sure he wants me to choose between believing in god and not believing. any help?