**spoiler alert**
The movie overall is nice but towards the end, it just feels like peter never learned from his lesson. He have 2 times to press the button and the first time, he choosed to give them second chance which to me is reasonable. But after May/梅姨 dies, he should have press the button (personal view).
If he had pressed the button, ye sure he will feel guilty or whatever, but at least he might not be forgotten by everyone.
These are my personal opinion.