What should I do guys???

Hi friends please I need your advice and opinion on this one... My bf best friend comes to my house late around 11pm to visit me knowing quite well that I will be the only one home but yet he still came. And I welcome him because he use to come to my place together with my bf... Then I asked him what made him come visiting late he said he came to see me! I was surprised and asked him that why and how... He started making advances at me until he even had the gods to touch my ass... I had to open my door and ask him to live. My question now is what should I do? Should I tell my bf or I shouldnt? Please help me here