From Dear Prudence advice column on slate.com (bolding is mine):
Dear Prudence,
I consider myself a moral person. I'm lucky to be married to someone caring and attractive, whom I love and who loves me back. We just had our first child. My wife has a sister who's been married for several years, has kids, and seems happy. She's also extremely sexy. My wife is beautiful to me, but she doesn't have the confidence to pull off "sexy" like her sister. A while back, my sister-in-law came over and we shared a bottle of vodka—my wife was pregnant so couldn't drink. Ever since, I catch glances from my sister-in-law that get my mind racing. She's paraded her body in front of me in bikinis all summer long. I'm not a cheating person, but I've also never been tempted before. I've tried to talk about it with my wife since we share everything. Now she feels I don't want her. She also doesn't think her sister would ever "want" me (not sure how to take that one). Hanging out with my sister-in-law and her husband is one of my favorite aspects of being a part of my wife's family. I don't want to disrupt anything, but I don't know how to carry this around with me. Would it be wrong to confront my sister-in-law about this and try to clear the air?
—Conflicted
Read the advice here.
LOL. This guy is a massive narcissist!