Really wanting to have sex with someone other than my fiancé

So me and my fiancé have been together 5 years we are high school sweet hearts we had our daughter last year and he's an amazing daddy I'm a stay at home mom which I love we bought a house last year it's like we have been married and we have an amazing relationship and I want to spend the rest of my life with him but lately I've been fantasizing about having sex with a guy I graduated with but I don't want anything els I simple just want to have sex with him just once it's almost like a bucket list thing ! I've been really completing asking my fiancé how he would feel about it I almost want to just be straight up with him and if he wanted to do the same I would agree to that as long as we used protection and it was only one time. Any one have any advice or has done it before I know I can't be the only one