Tbh one of the many, many things I love about my wife is we are super honest with each other about the fact we're both horny bastards. We're very attracted to each other and monogamous but we also look at other women and talk about them together. Like if we see a hot woman in a movie or a concert or on the street, we are unfiltered in our thoughts to each other. If we are out and about we keep the lewder comments for later at home ;)

At home watching a show she'll be like "I would let her sit on my face" and I'll be like "same!" LOL.

We're pretty lewd talking with our small handful of lesbian friends and they're pretty lewd talking with us, and the couples with each other. I get the sense the repression you talk about is a common phenomenon, and once we are in relationships or close friendships we let the words and thoughts free. I think your repression is probably part of why your fantasies are so frequent possibly. It will get better!