My husband wants me to go fuck someone else because turns him on

So we’ve been married for 8 years already three kids and he is been telling me that knowing I’m getting fuck by another man will turn him on, I’ve told him several times that I don’t feel too comfortable even tho it turns me on the idea of it but not actually going to execute it lol but it seems like he really wants it I just don’t feel safe or even comfortable being in bed with someone else other than him, our sex life is pretty good we use toys play roles you know is not boring but idk how to tell him I don’t want to exceed pass that what do yall think? Am I being selfish?