Offered MFM sex to my girlfriend and she immediately agreed to the experiment

My friend’s dad is very cool. When he first meets her friend, the guy wrests a cool watch from the dude for the right to live with the girl and use the house. Unfortunately, the adventure doesn end there because one afternoon the boyfriend sees his girlfriend sucking her stepdads dick. In response to angry remarks, he sends the boy to hell, and then fucks the girl with him, because the more dicks she has for sex, the better...