Have a straight forward, mature, sober conversation about it when you aren’t in the middle of an erotic moment together.
“Hey, the last few times we’ve hooked up, it feels like this fantasy has come up. Is this something you want to explore? I’m confused because I thought you were jealous of other women in the past.”
I would play with degrees and fantasy BEFORE you bring in another human. Another human is a huge X-factor, and you’ll need to do more communicating with them. Instead, she could dress up & pretend to be someone else, or you could try verbally including these fantasies into a scene.
Communicate, get clarity, take small steps, and talk after these scenes about how they affected you & your partner.
I mean, he is a reality TV star. Isn’t this how he lives?