My friend Cassie and I were both 19 at the time that her Dad was getting remarried. Her step mom moved into her house with her step brother prior to the wedding and thing were uncomfortable to say the least. Cassie was an only child and now an 18 year old guy was just living across the hall from her. It was hard to adjust to, but he was a nice guy at least. I teased her relentlessly as soon as I bet Ben (her step brother) because I thought he was cute. She repeatedly told me I was disgusting and I think it really started to bother her. One night we were drinking and I started up with the teasing again and I could see her face getting red. I pressed her on it and she finally broke and admitted that she thought he was cute too but that it was weird and that she really wanted me to stop talking about it.

Skip ahead nearly a year to after her Dad's wedding. The two of them went on their honeymoon leaving Cassie and Ben home alone. We obviously had a party, nothing major, but everyone got hammered. At the end of the night it was just the three of us and I started flirting with Ben like crazy. He was pretty awkward around girls so it was fun to see him get riled up. Eventually I leaned in and kissed him on the couch and started touching his crotch. Ben was obviously in heaven, but Cassie objected immediately. I stopped to Ben's great dismay. I told Ben that Cassie was just jealous because she thought he was cute. Cassie obviously freaked, but I cut her off and told the two of them that they weren't even related so they were making it weird for nothing. I grabbed Cassie's hand and pulled it to Ben's crotch. The two of them just stared at each other for what felt like an hour and then Cassie pounced on him. It was like I wasn't even there anymore. I left the room but kept watching from around the corner (obviously). They made out like crazy and then Cassie dropped to her knees and took out Ben's dick. He looked nervous but didn't protest when she put it in her mouth. She blew him for a few minutes before he exploded in her mouth. I'm guessing she swallowed because she didn't get up to go spit or anything.

None of us ever talked about it again so I have no idea if they kept it up or if it was a one time thing.