This is not about infidelity, it is about what may appeal to you about your husband. I may be that the qualities you find most appealing in your husband are the things that remind you of someone else. This is like being with your husband while fantasizing about being with someone else.
From another perspective, this may suggest a type of intimacy (non-sexual) you may have shared or desired with the departed or someone like him. I hope this helps.
"Are you bored with life? Then throw yourself into some work you believe in with all your heart; live for it, die for it, and you will find happiness that you had thought could never be yours." Dale Carnegie