I frequently fantasize about my wife's younger sister. She's a few years younger, thinner, and generally more attractive than my wife. She had a baby a few months ago and she's breastfeeding, so her breasts are so large and firm, it's a real turn-on. Sometimes she wears loose-fitting shirts, so when she leans over to play with the kids I sneak a peek at her full breasts. I try to be discreet so she doesn't notice. I have elaborate fantasies about scenarios I'd love to play out with her. If anyone knew they'd be mortified.