Nancy, you inspired me to watch "Unfaithful" again. I work at the Cinéma archive, so I can watch what I like on DVD, video and the greatest: In a screening hall. I watched it in my lunch break with someone at work.
How can one expect to live always with the same person? I find it virtually impossible. My ex-husband and I talked often of seeing other people for fun and at one point in our relationship we did that. This went on well for sometime, then we went for more closeness. Human nature is bound to be like this! How can it be otherwise?
One fabulous (and depressing) Bergman-movie is about this delicate subject. Three people meet on a tiny island and the wife falls in love. I can´t remember the title but you can find it in the Internet Movie data base. (Imdb.com)