I think that after 15 years of marriage that I am

I think that after 15 years of marriage that I am starting to bat for the other team. I'm so confused, my feelings are all over the place. The other night my friends and I had a girls night out... found some guys and ended up playing spin the bottle... I know it's a little weird for 45 year olds but sooo much fun. anyway, well it was finally my turn and it landed on my best friend. One thing lead to another and when I dropped her off at home that night..it went further. I don't know how to tell my husband. What should I do?