"Go ahead!" she urges you, "I want you to cum inside me! I want to see you when you get so excited you can't stop yourself!"
You fuck her as hard as you can, the base of your cock slamming into her pussy, as she pulls down on your cock. You feel your orgasm building powerfully!
However Silvie doesn't know your wife's trick for making you cum in the missionary position, and so ultimately you are frustrated and unable to have an orgasm!