Sex And Life

At what point in our marriage/relationship do we get tired of taking time out for sex? In the beginning, there seems to be so much passion and time put into our loving and then once real life settles in, things begin to change. Working, household chores, paying bills and having children are some of the things that make the change in our love lives. I have to admit, there were times that we went through that I felt that we still took the time to have that passion, but other times, it felt like he was just going through the motions. We were married for a very long time but it seems that even though the sex was there at the end, and quite frequently I might add, that he still found it neccesary to have other women. What happened to that sex that everyone reads about in books, watches in the movies and partially sees on the tv? Is that just something that only newlyweds experience and then gets settled down into something humdrum once real life sets in? Maybe I had just hoped that it was something that was lasting.