i really want to have a three way with my best friend and boyfriend

my (28f) boyfriend (28m) are mutual friends with my longtime friend (26f). i live cross country from her now, but my long distance best friend used to live extremely close by. since high school, we’ve had a friendship that occasionally turned sexual when we were bored or just felt like it. my boyfriend and i are meeting up with her for a vacation next month and i’ve “joked” about the three of us hooking up. he’s joked back “no. i can’t disappoint 2 women at once.” i can’t get him to take me seriously! she and i have hooked up with my previous longterm partner and it was great. there was never any jealousy and sharing has been something we’ve liked doing since high school. i really hope he’s into the idea or willing to watch or something. i think he’d love it if he gave it a try. i want to bring it up in a serious way tomorrow.