So confused! Please help

So my boyfriends best friend is always around! We have one night a week where it’s date night and no kid and every single time he’s there for a majority of the night. I don’t mind this but lately I’ve been thinking about asking my boyfriend of he can join us. Is that wrong? Also let me clarify that my bf has no problem with his “bro” seeing me somewhat naked and the one night even let him feel my boob. I just don’t know how to bring it up the topic with him. And I don’t want my bf to start thinking I have feelings for his best friend because I don’t. I’ve never had a mmf threesome and just want to try it

Update: he has said before that if we were to do this it would be with this friend