My in-laws were staying with us, and I thought they had gone out early shopping with my wife. I slept late on the weekend. I heard the car leave and thought the house was empty. I got up, put my bed clothes in the hamper, and walked to the bathroom naked. As I walked in, I walked right into my mother-in-law’s nude backside as she was toweling off after a shower. She began to topple over, and I stepped down to pick her up. I was twenty-four the time. She was a good-looking forty-five and pretty hot. Seeing her breasts and her shaved stuff caused me to get excited. I tell her sorry and go back to my room. She follows me and says, “It is okay. Don't worry about it. Give me a hug.” We are both naked, and immediately my excitement returns. She grabs me and starts to go to town. We have super hot sex including anal, and she promises not to tell my wife. I am afraid she will find out, and now my mother-in-law flashes me her stuff, wearing dresses, and has asked for sex from me a dozen times. I don't know what to do now.