Stay safe, Gav. Remember: Lush comes second!
I am in fact happily married -- literally, tomorrow is my 46th wedding anniversary -- and I flirt like crazy here, so your question feels directed specifically to me. (Though I'm not vain enough or delusional enough to believe that's true.)
Let me state it unequivocally and loudly: I love my wife right down to the ground. She has been The Best Woman for as long as I have known her. She is my partner in all the ways that she can be, and I am hers. I know in my marrow that she loves me. Does that mean that we fulfill every need for each other? No, don't be silly. We are two separate people, not one.
My marriage includes virtually no physical sex, and hasn't for about ten or fifteen years. Prior to that, we had a very satisfying, though unadventurous, sex life. We did try an "open marriage" in the first eight years of the marriage, but neither of us has had any other physical partners since 1977. My wife finds even the discussion of sex unappealing to the point of annoyance; that is, even a discussion about how we might expand our physical relationship is out of the question. There's never been a fantasy life to speak of -- we don't send sexy notes to each other or watch porn together, say. She dresses well, but never to be "sexy"; her lingerie is functional rather than provocative.
So. I still have sexual urges, and even if there isn't a sexual desire, I occasionally want to talk about sex with someone. Since my wife doesn't want to do that -- and actually doesn't even want to know if I do that with anyone else -- I talk (and flirt, and swap pictures with) some of my friends here. I have several Lush friends with whom I've gone way beyond simple flirting, but not in the direction of infidelity. Rather, we've exchanged a fair number of intimacies and secrets. You know, the way actual IRL friends do.
Summing up: I don't believe I'm a deceiving, lying hypocrite. You (the OP) can believe what you want.
Hint: There's a consonant in her screen name.