He is and they're. Mao and Kouichi have loved each other since they were kids, why do you think they kept showing the flashback? Kouichi was hurting Yuumi and he knew it, he broke it off apologizing to her.
She knew and told him "goodbye, "thank you for making me a little more courageous". If you can't look at that last scene between Kouichi and Mao and not realize that they're meant for each other then what series were you watching?