Perfect body Mistress is my wife's sister

My sister-in-law and I have a secret that I can never tell my wife. If it were discovered, we had an affair that would destroy everything...but I love both of them. My wife and sister-in-law love me...even though I know it in my head, I can't stop living a stressful life. Thrill increases excitement, and jealousy fuels sex. Besides, my sister-in-law has a lewdness that my wife doesn't have. She is the best woman to have an affair with. I wish this wonderful sex life could continue forever...