He's cheating on his girlfriend who's sleeping right next to him.
All women blame men for being unfaithful, but often they don't know both sides of the story. For example, in this case, the man tries to behave and be faithful, but it's his girlfriend's best friend who won't leave him alone. When she enters the room and sees the guy's penis, there's no going back. Even though the friend sleeps in the same room, she's not afraid of being caught, because it's more about the desire to enjoy such a big cock. She's an expert with dicks, she loves swallowing cum and knows very well how to drive men crazy, and apparently she's also an expert at sleeping with forbidden men who are next to their wives, because the bride didn't wake up at all.