I'm always compared to my sister who is smart and good at studying. What's more, my sister has a handsome and rich boyfriend and she brags about him. Seeing my sister acting all cute and completely different in front of him makes my resentment explode! In order to release all the frustration I've been feeling, I let my sister go out for a bit, locked her out, and then seduced her boyfriend and had sex with him, but I wasn't satisfied with that, so I showed my sister how I was having sex with him through the chain lock!