The woman I desire most

Good I wanted to share with you a story so I can relieve myself, the girl I'm talking about is my sister-in-law, she's the older sister of my girlfriend, she's a young 28-year-old girl, beautiful, cute brunette with a lovely smile, low face height, 1.55 meters tall, nothing more but has an incredible ass according to her small body, I don't know why I desire her so much, my wife or her younger sister is more beautiful than her, she's more beautiful in the face, a little taller, has nicer booty and I could do it with her several times with cum inside and all that, but since my girlfriend is very good, I don't understand why I desire her so much, my sister-in-law isn't an indecent kid, she's a quite centered girl, that's what I know, and I have no chance of ever getting her or making any proposal, I have too much to lose when she comes to my house sometimes she wears shorts made of fabric not denim and it highlights her booty in a way that makes me look at her without her noticing, I swear sometimes I have to masturbate because I desire her so much, when I do it with my wife I think about my sister-in-law and that's very bad for me, I can't stop thinking about her or desiring her and she's not more beautiful than my girlfriend, I don't know why I desire her like this, one day the boyfriend left her, he cheated on her and I couldn't believe it, he gave himself the luxury of betraying her and I'm dying to get her, to fill her pussy with cum and lick her booty without being disgusted, to put my tongue inside her and massage her vagina with my tongue until she cums, and this guy gave himself the luxury of leaving her, one day she and my girlfriend went shopping and I stayed alone at my sister-in-law's house, I couldn't help it, I smelled all the panties in the dirty laundry basket and the shorts that fit into her booty and I was disappointed because there were no stains or fishy smell, nothing, just a clean perfume smell, a frustration still, so I licked all the panties and had to masturbate. Incredible how much I desire her is incredible and I have no chance with her. I stayed with her at my house and we drank mate until my girlfriend came back from her mom's house and she sat in a chair like Indians do, crossing her legs. She was on her phone and didn't notice me looking at her and you could see her pussy because the shorts were so big or she didn't even realize it I did and that day I think I had sex with my girlfriend 4 times because I got so hot. I don't understand why I desire her so much, my girlfriend is better but I desire my sister-in-law a lot. Is it because one always desires the difficult? The impossible? What can't be had? I don't know. Thanks for reading my story.