Tried To Stop The Wife Swop

We were with two friends , husband and wife.
We had all drunk too much , when I jokingly suggested a wife swop.
The husband was all for it and kept pushing the idea. After more drinks and more pressure, my wife finally agreed, although his wife did not seem too keen.
Then suddenly her husband grabbed hold of my wife’s hand and took her upstairs.
I then kissed his wife, and Tried to touch her breasts but she said no!
It had only been about three minutes or so I said I would go and tell my wife and her husband that the swop was off.
But when I opened our bedroom door I could not believe what I was seeing!
My wife was on the bed, she still had her top on, but was naked from the waist down with her legs open!
There was a ripped condom pack on the floor he was between her legs, jeans and underpants around his ankles and his naked bottom was pumping up and as he fucked my wife!
Stop I said pathetically we are not swapping now.
He said panting, you might not be but I am now fuck off !
I Looked at my wife but she just turned away from me!
I left, it was an awkward wait downstairs until they had finished about 5- 10 minutes later.
When they came down nothing was said and they left.
We never spoke to them again.
I said to my wife that I was disappointed that she had let him start to fuck her so soon, but she said I was pathetic because I didn’t pull him off her!
She even admitted that she climaxed a little with him!
I still wonder why she let him up her so quickly.