I would like to see "don't do it man" guys in the same situation.
I guess after so many years things do get old and NO MATTER how much you love your partner there are situations when you desire another person. Most of the time it's only a physical attraction, however if it's more than that it may turn into an affair or desire to be with other woman (man) more than once.
I think a talk with your partner about "spicing up" your sex life would be an option. And remember one thing too:
"LIVE EACH DAY AS IF IT'S THE LAST ONE, AND GO TO BED WITH NO REGRETS!"
You are on your own...