ok, so you said no guys..... but what happens when she wants a threesome of her own with guys? You gonna say, ok, you go off and have fun, I'll see you when your done? I don't think so. Men are so double-standarded (to coin a new phrase) about this.
Your not thinking of your relationship, just your cock. No matter who thought of it.
If I decided to jump off a cliff, my other half would try to stop me. He wouldn't say, cool idea babe, just cos I thought it up.