Videos And Sharing

According to my wife before we got married, she'd had six lovers before she met me.
Recently I saw a couple of videos when my wife was twenty two. In one of the videos it shows several men taking turns to fuck her and at one point three men are fucking her at the same time, mouth, pussy and arsehole.
The second video is of one of my wifes old boyfriend's and they're out at a car park, which looks like it's close to a reservoir. He's fucking her in his car while filming and there are other men watching and wanking.
You don't see the other men have sex with my wife, but at the end of the video she's covered in cum, and you hear her boyfriend say "Four of them fucked you".
I've watched both videos several times over and can't stop masturbating whilst thinking of her getting fucked like that now.
One of the guys in the first video has a really large thick cock and when she's bouncing on his dick, you can clearly see the joy in her face as she orgasms.
My wife who's very pretty and so fit, obviously has had many many lovers. I don't mind at all, in fact it turns me on more than I care to say, that she's had lots of men fuck her. And the real reason I guess, is because I'd love to watch her being fucked by a guy with a really big thick cock.
The thing is, she doesn't know I've seen the videos of her, nor does she know I'd love to share her with another man.
My problem is, how do I bring up the subject. And how do I explain it turns me on so much thinking of other men fucking her.