My thoughts about another man

I am happily married to my husband for several years. He is my absolute best friend. I care deeply for him and he for me. We are an amazing team to each other and our kids. Our sex life is extremely enjoyable. I can tell him anything and I feel close to him.
Here is the problem- I find myself thinking and fantasizing about another man frequently. I enjoy the attention he gives me at work and I try to get attention from him. I have told him straight up I’m married and have kids and happily married so we are absolutely not close like that in any way.
It’s my thoughts I’m having a problem with. My mind keeps going back to thinking of him, what can I say to him, how can I be funny etc. it’s exhausting because I don’t like those thoughts morally but it’s fun to fantasize about.
I have tried thinking of my husband and all the things I love about him when I start thinking about him but obviously it hasn’t worked enough to stay out.
I need advice of what to do. I don’t want to be filling my brain about another dude. It doesn’t feel honest to me and I live and adore my husband! Why is this happening??