This is actually a documentary film that has its own website and trailer. You can order the DVD for $20. I saw part of it at my mom's last weekened, and its really an amazing film. While it doesn't touch on infidelity per se, it is inspiring and insightful and makes you want to write a book, climb a mountain or go back to school...it was awesome. I will order a copy and watch it once a week, to keep myself on track. Its about the wisdom that comes with life and with age.
One part of the film I do remember pretty well was a woman commented on her marriage, and why anyone would quit a marriage and quit discovering things about their current spouse, and start all over again with someone new. She said its like quitting in the middle of the journey.
But I guess that's assuming you are with someone that has a sincere interest in growing with you, and marveling at the changes in both of you, and doesn't just have an interest in themselves.
Anyway, the documentary was inspiring to me, and surprised I never heard of it sooner. It came out at least a year and a half ago.