He treats her like shit. Every tine he sees her he says the most horrible things a human being can say to another, and behind her back he "loves her so purely"….like that matters.
How can you make someone feel like the ultimate sh*t and still say that you love them and you can't live without seeing she's safe. But because the female lead is another brainless and spineless female in front of the male lead and lets him treat her worse than garbage, in the end it will be a romance admired by everyone…..so "normal and heartwarming".