That's because it brought him back to right before he...what happened to him anyway? Did his mind get transported back into his body in the past?
Was it all a hypnotic illusion that all happened in a blink of an eye that came from the shock of her gentle caress in contrast to his brutality, causing him to question everything he thought about relating to her and the world?
Actually, I like that. I'm going with it. Though it still doesn't explain how she's able to communicate with him in that world.
Besides, he stops immediately, and then it shows that kid coming out of the sea, seeing them asleep side by side with their pinkies crossing for an "awwwwwwww" moment, so it's obvious that he really cares about her in the end.