I can't get her out of my mind, but I know that if I act on my feelings it could end in disaster. I don't want to lose my family. I am very frustrated and I sometimes think that I should just take a chance with her. Maybe it will get her out of my mind. Please help me before I do something I know I will regret.
If you act on your feelings towards your wife's sister you will not only destroy your life, but your wife's family too.
It is impossible for you to have any future with her sister. Believe me, the truth would come out eventually.
Perhaps your sister-in-law is jealous of her sister and is trying to destroy what she has.
If she makes any inappropriate advances towards you, you must tell her in no uncertain terms that she must leave you alone. If she persists you must tell your wife that her sister is putting you in an awkward and uncomfortable position and your wife must speak to her.