You will find that romantic love diminishes after two years at most, and if your sex life is tied solely to those romantic feelings, you won't be having any sex. So for me (and virtually all people I know that have been married more than maybe 5 years) your imagination is very helpful. What you should be hoping/looking for is someone who shares your values with regards to where the lines are drawn. I may have fantasized about another man, but I wouldn't move beyond that because I am just not the type.