Wife and girl friend

[rebbonk]

I walked in from work today and my wife was sitting on the sofa with my girlfriend.

I said, "What's going on?"

"You tell me?" replied my wife.

I said, "I don't know, you're sitting on the sofa with a stranger."

"A stranger, hey?" shouted my girlfriend, "I'm no stranger, we've been having sex for six months!"

I looked at my wife and said,

Spoiler:

"Is this true?"