Affair With SIL

My SIL is 4 years younger than my wife and is the most desirable woman on this planet for me. I have been lusting after her ever since I first met her. Back then she was in a serious relationship. But last year she had a very bad breakup and she came to stay with us for few months.
Long story short, one night she and I were alone drinking wine and just talking about stuff. Eventually the conversation turned to sex and it turns out that my wife has shared many details about our sex life with her sister. I'll be honest I'm pretty average size guy but I got good stamina and techniques. SIL told me about her sex life with her ex bf. According to her he liked rough stuff more and she never really had any softcore passionate sex. After few awkward pauses and nervous laughter, she jumped onto my lap, her butt rubbing my dick and her tongue deep in my mouth. So we ended up having a very long and passionate sex, just like she wanted. We've been doing this everytime we get a chance. I still love my wife and want to be with her but there's something about the SIL I just can't resist. The feeling I get when I'm on top of her, our faces so close, her eyes filled with passion and pleasure, her warm and soft body pressed under me, and when I'm inside her doing slow and steady strokes. I don't know how to describe this but her pussy feels so warm and cosy, the way she grips me tightly, and the squishy sounds it makes with each stroke is like a d*ug to me. She's going to stay with us for few more weeks I don't know what happens after that.