Recently I shagged my sister in law Katie at a party we held at our home for my wife's birthday. Katie stayed over and I swear I honestly thought she was my wife in our bed. Messing about in the dark, she'd covered herself in our quilt, but offered up her pussy and arsehole. I took up the offer and fucked both holes thinking my wife and I were having a sneaky sexual break from her party. Only when I came deep up her arse, did I hear Katie orgasming, then her telling me she was amazed how much larger my cock was than her boyfriend's. I freaked a little, but had shut up as we both heard someone using the bathroom next to our bedroom. We obviously didn't say anything when we got back downstairs and nothing has been said since. However my wife has told me Katie might be calling by when she's in France shortly. There's no reason for her to call by, other than a short text she sent the other day. It says 'Looking forward to another duvet day. Aren't you x'. My wife goes over to France for three days next week and I can't say I won't be tempted.