First time I did it to my wife, my friend had just pulled out and had cum a lot. She was laying on the edge of the bed on her back and it was leaking out of her pussy. She asked for a towel and I said we didn't need one. Then I went over, spread her legs and dove in. We had never discussed it and she wasn't expecting it. It turned her on so much she came again (after multiple orgasms with my friend) hard after only a few seconds. She loved it. Later that evening, after we called it a night and went to bed, I sent her back down for another round. She rode him cowgirl, then came back up stairs full and sat on my face so I got the full load. She had multiple successive orgasms as I ate her. Unfortunately, that was the last time I got to eat her after she fucked him. After I left for work in the morning, she fucked him one more time, just for herself. That was her last time, despite my encouragement.
Reference the attached picture, my friend had pulled out at 10:57:46. Here she is, tightly gripping my hand as she convulses in orgasm 30+ seconds later. My friend is standing on the right blocking her face.