An Afternoon At The Office

I'm engaged to a wonderful guy, but work has its perks too. Last week, it was just one encounter with someone from the store, I'll call him Mike. We both knew we shouldn't, yet there it was. It wasn't about passion or love, more like stress relief and comfort in an unexpected place. The details are fuzzy, but I can feel that rush of adrenaline still when I think about it. Is this normal? Should I just focus on my fiancé, or should I address what's been stirring inside me? What would you do?