when a man/woman are married and have sex with another man/woman.
I'm having an affair with the daugther of my friend.
by WEHG October 04, 2006
something that destroys people's lives and something you should always refrain from having because you will realize eventually how stupid it was
He had an affair with her best friend, and when she found out about it, she instantly divorced him and they never talked again.
by pbfn4ever-51 May 22, 2011