It's from today's Apple event, and the scene is a young couple moving into a house together. The girlfriend video calls another man and starts chatting, and the boyfriend is left looking at a video of this other man on the phone's second display.

The joke is not "it looks like the girlfriend is cheating on him", but rather "showing a video of the person you're calling on the display facing away from you has no obvious use cases except for cuck play"

The woman has an interaction with the person on the screen while it is implied that the third person just off-screen has to sit and watch.