Because he loved him from the start.
It's so sudden because it's like a ballon that's been getting bigger for a decade just exploded. They both completely misunderstood each other. And rather than trying to communicate, they hurt each other more or less voluntarily. And so the cheer disbelief and euphoria of "there never even was a pb" is why it feel sudden for us readers
yeah that’s fair, maybe it’s just how i’m seeing it. but even if they did like each other from the start and the whole time apart just messed things up, it still feels kinda sudden and out of place. esp considering uke was running away from seme just a couple chapters back.
seriously, the art is really nice and i’ve grown to appreciate the complexity of the characters but what the hell is happening with the recent chapters? am i missing something? how could he fall in love with heeso that quickly lol