Oh I found out about the Wife first. 3 months before the GF but my gut knew it wasn't the whole truth. I said to him repeatedly. You are keeping something from me. I know you are and he swore blind he wasn't. I accepted this but kept looking online for information.
Then I discovered the girlfriend when I asked him about the girlfriend he fobbed her off as a friend. I accepted to him but I knew it was her.
I discovered this via social media. It was a post on new years day. I saw it at 6am. That confirmed my suspicions.
I commented on the picture first nothing ragey. Then sent her a private message with much more detail and what I knew.
I then screen grabbed the picture. Sent it to the ex and demanded to know what the fuck was going on so she got the messages before he had chance to concoct a story.
She called me with him in the room, my insistence I speak on the phone so I knew who I was talking too and it all came out.
I raged at him called him a cunt a liar a cheat and arsehole. He was of course just muttering 'twat, you know that's not true' when I yelled at him we had had sex recently. Told the GF I would message her all my proof we were together and I did. Every last bit. Including my call log dated and timed with length of calls to him. Calls when he said to her he needed to go out 
I also told the Wife what had happened. I didn't want him grovelling back to her. In another life me and the wife would be ace friends!
I messaged everyone of the friends he had told me about and anyone with his surname in his friends list with a shortened version of events. My very lovely friend set up a public facebook post linking all the accounts he had, the truth and with a fabulous meme so anyone could search his name and find it.
He received so much abuse and angry messages from people he's hurt he's shut down his social media and has no one. Literally no one.
his wife confirmed this. He confirmed this. His friends are disgusted they too were lied to. I've recieved messages from a number of them I haven't replied to.
My battle scars are going to take a long time to heal but I destroyed him like he did to me and to her and to his wife.
Moral of the story, don't piss me off 