I have done it unintentionally without realising it. My partner would usually never let me fuck her after she has been with her lover, but she always wanted to fuck me as soon as possible after I had been with my mistress. So I have rarely enjoyed her creampies made by her lovers.
However on one of the rare occasions when I have it happened like this. I arrived home one evening after being out all day and found her already in bed. So I undressed without switching any lights on and slipped into bed alongside her. She rolled over in her sleep and put her arms around my neck and clasped my thigh between her legs and gave it a squeeze whilst murmering something in a sexy voice that I did not quite catch. Then she woke and said "Oh! its you!" and turned over and went off to sleep again, leaving a wet patch on my thigh.
By now I was really hard and snuggled up to her and reached down and slipped a couple of fingers into her pussy. It was really wet. I slid my fingers in and out and then licked them and slid them in and out again. She purred, half asleep and pushed her bum against my fingers. So I then slid my cock in her. She was so creamy. I slid in and out of her slowly at first and built up speed until I came. I came several times that night in her as she lay half asleep.
The next morning she told me that her lover had been with her all day and into the evening and had fucked her so many times that she lost count. When he ran out of cum he went down on her and used his tongue. As she described her day and all the positions he fucked her in we both got very horny and after a while she opened her legs and pulled me onto her. I slipped into her without the need for any foreplay and we both came together really massively and added more cum to his.