Personally, I wouldn't tell my close friend about it. I believe most straight guys wouldn't tell their friends the details how he fucks his gf/wife. I guess he won't tell you about his sex life too. Most of guys I fucked are married w/o kids. I'm sure no one would know they loved getting fucked by me! One of my best friends used to be my fb and I don't even share anything about my current sex life with him now. Of course, I won't risk to share that with my future gf/wife. To be honest, I'm not attracted to any of my close friends at all now lol. I guess the reason why you wanted to tell him is because you are attracted to him. IMHO, I don't think it's worth it to lose the good friendship. You can always find an attractive sexy safe sex partner. Like @bi2 said, enjoy your bi sex privately and keep it private