I think I'm in love with my wife's sister
Oh, dear, how did you fall in love with her?
Well, I don't really believe in love at first sight, but I did fell in love with her soon after it happened.
I think it's morally wrong to be in love with anyone other than your wife, especially if it's her sister. You should really try to brush your feelings aside and focus more on your wife.
Nope, I feel happy.
I strongly suggest you move on from this. You're spouse, her sister and you will be happier in the long run.