Ever since my wife and I were dating, her sister (who is mind blowingly sexy) and I have had a flirty relationship including ass slaps, hugs that last a little longer then they should and playful touches. My wife has always been a little uncomfortable with how flirtatious we are, but just chalks it up to her sisters playfulness... and it is what it is.

This summer at a family get together, I went to the basement to do a load of laundry and I noticed a pile of her dirty laundry with a frilly thong sitting on top. I lost the fight with my inner demons and took the thong and sniffed her sweet pussy juices that had soaked into it from a day of wear as I jerked off in the bathroom. I don't know if it was the taboo or her scent or both, but I had one of the strongest orgasms of my life.

When I was done with them I took a gamble and left them on the bathroom floor hoping my SIL would notice something amiss. Later that evening I got my answer, when I was folding my laundry her thong was mixed in with it. I was incredibly turned on, but I don't know where to go from here... how or should I push the boundary further with her?