My husband won't shut up about a threesome.

I have entertained the thought before, don't get me wrong. I just won't jump into it with strangers like craigslist. But he just won't shut up about it. He brings it up every time we have sex. I'm tired of hearing about it constantly. And when I tell him to let it go, he implies I'm a prude.... I'm a prude because I don't wanna hear about how sexy it would be every 5 seconds?.... starting to feel like just me instead enough for him..... sorry needed to vent.