Bonus if you're there when she does it.
My wife said this to me one night and this is exactly what I asked her. That night she told me about another guy she use to “play” with his cock before we started dating. This was the first time she had ever mentioned another guy’s cock.
I love watching you. I watch your lips when your sucking my dick. I watch as my dick slides in your pussy. I watch your tits as they bounce up and down as you ride my cock. I watch your face when you have your orgasm. Why wouldn’t I want to watch you with another guy? I could experience all of this in such more detail. The best part I still get to have you when your done with him.