Every person has his limits and sometimes people have to overcome those limits.
That day the dude had to overcome his sex limits and to make his girlfriend fuck a stranger in exchange for a sum of money which would help him to gain financial independence. The dude simply had no other way out or at least this is what he told his girlfriend. Luckily for him she believed him and agreed to place her pussy at the disposal of a rich stud and to serve his dong with her plump lips in front of her boyfriend.
Oh this movie is a very spicy one and you are welcomed to enjoy it.