It was awhile ago and I was still in high school.
I was 16 and my brother was 17. I was doing laundry one day during the summer while our parents were at work and his clothes were still in the dryer. Being a good sister I put his clothes into a bin and brought it to him. I opened the door and my brother was completely naked with headphones on, masturbating to some porn he had on his computer. I must've stood there for five minutes before he came, took off his headphones and turned around and we made eye contact. He threw on some clothes and begged me not to tell our parents. I left without saying anything. Later that night after dinner and without saying a word to our parents, my brother went to my room.
He told me, 'Thank you,' and was about to leave before I stopped him. I was horny the entire day and told him to show me again or I'd tell our parents. He was nervous so I sat him down beside me on my bed and he must've gotten more comfortable because he took off all his clothes in no time. I took mine off too just to show him that it was okay. That got him hard. I told him to start doing what he was doing before and he did. After about 30 seconds he said he was going to cum and shot it all over my chest, face, and hair. He said to me that because he showed me, I should show him, it was only fair. So I did. I started to finger myself and eventually pulled out my vibrator that my aunt got for me. That got him hard again, so I told him not to do anything until I was finished.
I'd never come quicker. He was hard and I was still horny so I grabbed his cock and started to stroke him. He closed his eyes and must've drifted off because all I remember was him breathing really, really hard. He came again, this time into my mouth because it was about 3-4 inches away from his penis. I was still wet so I told him to finger me and he did so, so enthusiastically. I came and covered his hand in juice. That was the end of that night because it would've been suspicious if we started spending so much time together all of a sudden.
It was about a few weeks after that that he popped into my room again and asked if we could do the same thing. I was so excited that all I remember doing was taking my clothes off. While he fingered me, I closed my eyes and just let him do his magic. This continued for about two years until I moved out for college.
This is still happening from time to time. I'd come over when his girlfriend is gone, and he'd come over when my boyfriend is gone. I've never been closer to anyone.