Why did cupid wake up from his asleep and leave psyche ?

Psyche had never seen Cupid. That was part of the deal. Cupid warns her that if she should ever looks at him, he would leave and her unborn child would become mortal instead of a God. Psyche’s sisters were jealous of Psyche's good fortune. They convince Psyche that her husband is actually a monster. Psyche decides to take a peek at Cupid while he is sleeping. She grabs an oil lamp and a knife (in case he is a monster).She sees a beautiful winged angel dude! The oil spills onto Cupids shoulder and he wakes up. As per the deal he leaves Psyche.