My Sister's Flirty Friend

I broke the cardinal rule and slept with my sister's best friend. Granted, I'd just found out that I was now a single father to a three-year-old little girl and was low on willpower. It should also be noted that there's been sexual tension between us for years. There's no way it would be a surprise if anyone in our small town found out. That is if we were telling people, which we're not. We're in agreement to keep our affair a secret, especially since neither one of us do relationships. You've probably figured it out already, but things didn't go as planned.