After Falling in Love with My Brothers and Sisters

I have been in a relationship with my good brother and sister for a year. I was thinking about how to confess to my brother that I had an affair with her sister. But he said that his sister was getting engaged to her boyfriend and asked me to come and witness it. How come I didn't know about such a big thing? At the dinner, the girlfriend and her boyfriend fed each other, showing their affection. I smiled: "In that case, I'll call my girlfriend here too." But she couldn't sit still. This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.