Passion does fade as time goes on. Towards the beginning of a relationships both partners want to remain together all day they text, call or physically try to be with each other all day. I personally have not been in a relationship therefore, I cannot speak for myself. However, many of my friends have and i’ve experienced their behavioral change they slowly apart themselves from close friends thinking they are the only two in the planet. From what i’ve seen when family members get married and how they are now it seems that later on in the relationship they still love eachother, but do not need to express it every second they are together. For example, at parties there is no need to always be together they interact with others.
I cannot think of anyone who I may know who show passion after several years of marriage. However, love has no correlation with passion. Its a new different love to explain better it’s just like love is expressed in different parts of the world. Love is the same regardless where one is, but everyone is at different phases of love.