Very Bored one rainy afternoon

I'm Alex 23 recently I was home with my sister Joanne 25 and it was pouring with rain. Nothing to watch on TV or the internet as everything was down due to the thunderstorm. Power was also out and I just asked Joanne for sex to pass the time, expecting No as her answer. But she said Alright I feeling horny and I'm on the pill and it will pass the time. So not wanting to back out, I went with her to her bed and I fucked her twice and then we had a nap together and then more sex. It was after 9 pm that night that the power came back on. Our parents had rung on the landline phone which was the only thing working that afternoon and said they would stay at our grandparent's place till the next day as there was some flooding. So Joanne and I slept together all night and even fucked again in the morning. We finally got out of bed around 10 am and showered together and had only just got dressed when our parents arrived home. Since then I have fucked Joanne a few times and it seems that she likes me fucking her. But we still date other people but aren't backward in asking each other for sex when we are alone.