I (30m) have a taboo thoughts for my sister in law (31f)

Since i found my sister in law nudes (by accident) and i can’t stop thinking about fucking her and licking her beautiful meaty pussy and suck on those big rounded tits of her.
I jerk off to those nudes everyday thinking what if i can get her in my bed right now and how i can please her.
She’s very kinky and likes a lot of stuff (i know that from her nudes and masturbating videos) she does a lot of pinching and slapping and licking her soft nipples and even grinding on plushies, she is really perfect and hot.
I even can’t have sex with my wife (her sister btw) anymore i don’t see her as attractive as she is.
Please help me on how to approach her or take any steps towards that without running my marriage?
Fyi, i started to talk to her about how her sister don’t do much in bed and i’m not happy and i even stopped caring about have sex with and all of that and i just satisfy myself with porn and all of that (we are close to talk about those things) but she keeps telling me that everything will be alright between me and my wife she don’t reject me but she’s telling me the things everyone will be saying in this situation that’s all.