Bad writing.
Seriously, what was the motive for these 2 girls actions?
They lure him into the bedroom and **** him, whilst he is under the impression they are of age....
The next day they lie and tell him they are actually under 18....(Why, I have no idea)
So, for the rest of the film we are led to believe that they are punishing him for apparently being a pedophile.
But at the end, they reveal that they actually ARE of age so.....Why did they do it?
It's not like he thought they were under age and did it anyway, he thought they were old enough!
Sure, the guy cheated on his wife but why would the 2 girls give a sh!t about that?
What was their motives for doing all of that sh!t?