My cute sister sucking a cock and getting fucketd

My sister and I have been very close since we were kids, and I’m kinda close to her best friends too and know some of her schoolmates, etc.
We’re in high school, she’s one and a half year younger than me.

She’s a kind of quiet girl, you wouldn’t expect anything dirty from her, I do always realized that she was beautiful and realized when she was developing a nice ass and nice legs but never thought anything sexual of her. Always saw her naked or in underware like most families do, no big deal.

One day, one of her best girl friends told me that she was planning to fuck later that week, it got me totally inadvertent, it was so unexpected from my little sister! even for me! having such good close friendship. I couldn’t believe it, didn’t want to believe it, the fact that my cute little sister, the one I helped to walk when she was a baby, to talk, and all that, was going to get fucked by an idiot that I didn’t know!
It might be normal if you see it from an external point of view, but not for me, she was the treasure of the house! everyone trying to take care of her.

At first I wanted to ask her, and tell her that I wasn’t going to allow it at all, but then it made me really really horny, after all those family thoughts, just thinking about it made me hard, made me dream about her getting fucked by a guy she barely knew, enjoying her (even acknowledged by me) beautiful thin-but-tasty body, big beautiful ass and killer thick legs, got all my incest fantasies I didnt know I would have at 100%.
I waited ’till she came back from school that day and we talked about ourselves but she didn’t mention anything about it, but i knew it was true because her friend never lied to me or to her.