"I don't want her to die" he said after killing her a great amount of time-

THAT'S THE POINTTTTT IT'S LITERALLY HIS CHARACTER DEVELOPMENT

But like imagine she never came back in time she just dies

Then he wouldn't have come to love her the point is literally he finally got to know her now and fell in love with her

If he was in love with her from the start, the story would be cliche and wouldnt be as interesting