Muscle guy fucks his girlfriend's little step sister and they end up discovered

I arrive to greet my girlfriend and I find that her sister is visiting and she is so beautiful that I can't stop looking at her and I look for conversation to please her. After a while we are together I notice her morbid look and I take the opportunity to kiss her, we get so hot that we end up fucking wildly in the living room and her step sister discovers us by the screams of pleasure.