I knew that it was a bad idea to tell him about the newest thing in my life. It's not something shocking, or extraordinary in itself, but, for me it was a big event. I had sex! My brother hasn't, yet, so he was very curious about it, not being stopped even by the idea that he asks his own sister about these things. I felt flirty and wanted to brag about it, by this fueling his curiosity. I assumed he will have a lot of questions, we used to bet who'll first lose their virginity. I'm in a relationship, he knew that but probably imagined that we, my boyfriend and I, watch movies and have intellectual discussions... We fuck like rabbits, of course, like every young person that discovered sex and is amazed about how much pleasure can be felt. As I was telling him the details he wanted to know (out of pity, mostly) I noticed a change in his underwear. It was like his penis was becoming erect! I couldn't believe my own eyes, but continued to fuel his curiosity, wanting to know how far he would go. Not only that, but I got curious myself about the bulge in his pants, it seemed quite big! We teased each other constantly these years, and pulling-clothes jokes are common between us. He wanted to take a selfie and pulled my top, revealing one of my tits. I hope I'll remember to delete that pic, for safety reasons. Now he began touching himself, and -probably- his penis was already fully erect, tight in his underwear. It was like I could clearly see it, only blocked by the fabric... He knows me well enough, knew immediately what's in my thoughts and took it out, proudly rubbing a thick, long cock. It was also wet. I just couldn't resist and I touched it. He kept his hand over mine for a while, squeezing hard. It was so natural, and... hot, with my brother. I jerked him off a bit, getting hornier, told him I want to suck it. I craved for it, I needed it in my mouth right there. I laid on the bed and let him mouth-fuck me, opening my throat and deepthroating it to the balls, licking, kissing and letting him know how horny I felt. I worshiped that cock, wrapping my mouth around it like with a lollipop. I took my jeans off, and he finally gave it to me! I rode that cock two orgasms long, until I almost lost my breath! I cuddled him, rubbed his cock again and edged him a little before convincing him to fuck me again. He wanted to cum badly, barely postponing that big orgasm waiting in line! He fucked me again, being on top of me and making me feel dominated and obedient. Then I kept my promise, like the good sister I am: I made him cum in my open mouth! It filled my mouth and drooled on my chin and neck. He was not a virgin anymore and very, very happy!