My [M]36 wife [F]32 got secretly creampied by my best friend [M]36

My wife and I have been having a bit of fun with threesomes and similar for a lot of years. Mostly flirting online, sending Snapchat videos ect to strangers, but had a few threesomes with both genders.

Background story:
Last weekend, my best friend through 20 years stopped by and we had some drinks and had fun. Let’s call him Michael for the story.
Michael and my wife have fooled around before, she gave him a blowjob once, they had sex another day – all of this is 8-10 years ago, and nothing sexual has happened between them since.

Fast forward to last weekend. My wife has been craving him for a while, wanting to feel his dick again. I allowed her to do what she felt like, and by God she did.
We were outside in out terrace having drinks, playing board games, every time I left, she kissed him. I had a hunch, so one time I went to the bathroom I peeked out the window and saw her sitting on him, him obviously fingering her and them kissing each other passionately. My dick got crazy hard while I was watching them – none of them knewing I was there. When they stopped I went outside, pretending not to know what they were doing.