Secretly observed while showering..!

My stepsister was visiting me with her boyfriend over the weekend...her new lover is pretty sweet...we had a great evening. When it went to bed, I heard the two fucking loudly ... I was curious and took a look into the room OMG my SSister was just sucking his big part, then he took her from behind with hard bumps, I stood at the door and did myself, our eyes met briefly then I disappeared again. The next morning I was just taking a shower and I was doing it with the shower, slowly the door opened, there he was with a huge latte....my SSister was still asleep, then I took advantage of the situation and fucked him! It was so extremely cool to know that she could come in at any time!