I want to try a new kink with my boyfriend but I don't know if I should or how to ask him about it

Me and my boyfriend have been trying some knew things, nothing too extreme though. I know for certain I'm bisexual, and I'm pretty sure he does too. He fucked me in my ass, and I absolutely love it but I have this fantasy of fucking him with a strap-on or just sucking him off while he fucks himself with a toy. I would be open to having another person (of either gender) with us during it, but he already said he dosent like the idea so I wont push the idea anymore. I just want to see if he would like somthing in his ass, I've heard guys say how being fucked in the ass gives you the best finish and I would love to hear and see my boyfriend be fucked and have the best nut ever.

Overall, I want to ask him about it but I dont know if I should or if I should just forget the idea? Any advice??