Telling your friends

I'm in grade twelve and my boyfriend graduated last year. My best friend was talking to him one day to try and get him to get her lady products but didn't want her ex to know so she tried getting my boyfriend to be alone and ask so she said that it was about me and my bf said well just tell me infront of him I tell him literally everything which sort of makes me uncomfortable to know that this guy knows everything about my relationship and lately he's been really nice to me I have only told my best friend about me and my boyfriends interactions so to my point what are your opinions on your significant other telling their best friend details on sexual interactions personally I don't tell my best friend everything so I feel weird about her ex when he knows things...