I had been in the babies room, taking care of our little girl, while my wife said she wanted to lay down. After the baby went to sleep, I walked down the hall to our bedroom, where the doorway was partways open. From there, I could see the end of the beds' mattress rocking slightly, and I heard the creaking of bedsprings. Peering through the open door, I saw my wife face down on the bed, and naked as a jaybird. Her ass was pumping up and down, grinding her pussy against a pillow she had between her naked thighs. My wife had masturbated like this for me countless times, but this was the first time I had actually walked in on her doing it when she thought she was alone.
There was something so erotic about her humping without her knowing I was watching! So I quietly unbuttoned my jeans, and pulled out my dick. And so I stroked off as I watched her hump her pillow faster and harder, till she made herself cum. And so did I - quietly all over the front of my pants. She remained face down in bed when she was done, as if going to sleep, allowing me to sneak off to clean up in the bathroom.
Being that she's remaimed silent on the subject since then, I don't think she knew I had been watching, and I feel a little creepy telling her I had spied on her without uttering a single peep, because she's never said anything about it...Still, the door was open...