I want to ** my sister in law

I've been with my wife for several years now and have always thought her sister was absolutely stunning. Big plump ** a perfect **. Amazing hourglass figure.
It's hard to tell if she's into me or not. She's made comments about how small her husbands ** is almost hinting at me to disclose the size of mine. I find myself ** to pictures of her regularly. I have used her dirty ** to ** with wrapping them around my **. And also licking her sweet juices from the **.
I have the urge to be inside her so bad I want to bury a load of ** deep inside her.

How can I try and persuade her that we should have fun?