It's not like it was implied they're a couple in this lifetime bro... It was meant to be wholesome that he gave her up and she was able to be reborn without memories and live another life and he's fulfilled to watch her be happy from afar. Chill.
Sorry, the version I know is the novel, and there their encounter in this life still leads them the same romance route. Guess I forgot the manhwa can be interpreted differently ╮(￣▽￣)╠my bad/gen
Now damn that's creepy. Gives Nanatsu No Taizai vibe and that already gives me enough ick.
If she wasn't FOURTEEN I would've actually enjoyed that ending