[M4F] Showing my wife’s sister what a good guy can do

Looking for a semi-detailed (2-3 paragraphs on average) with a literate person. I 26M want to play out this fantasy I’ve had lately. Basically, my wife and I have a great, new marriage, and our life is fantastic together. However, she has a younger sister (19) who has a shitty boyfriend. He’s just not good enough for her. He has stopped putting in any effort, and he doesn’t try to make her feel special or loved. She’s frustrated with him, but she’s also convinced herself after being with him for a few years that she can’t do better.

My wife, meanwhile, has been telling her sister about how wonderful I am, both as a husband and as a lover. She’s told her sister that she deserves a man more like me, who will treat me right. So, one night when she’s staying with us (maybe over spring break or something), while my wife is away/asleep, she (you) get curious decide to take her advice a little literally. Maybe you’re trying to prove your sister wrong…I can’t be that good…can I? Or maybe you’re just jealous after hearing her go on and on.

I’ll initially be somewhat reluctant, but since I’ve always found you more attractive than my wife, it doesn’t take too much seduction to get me to “help” you see what you’ve been missing.

Kinks: cheating, dresses/skirts, stockings/tights, detail, literacy, blowjobs, dirty talk, seduction, comparison, clothing descriptions, kissing, cowgirl, doggy, lifting/pinning, spanking, moans, mild degradation

Limits: raceplay, anal, scat, cumplay, futa, extreme BDSM