Taking action for once? The guy just CONFESSED, which is more than Hikari ever managed. If Hikari doesn't want a relationship with him, she should just say so instead of whining about Yuu daring to have a prior relationship that didn't involve her.
Where did Hikari whine about Yuu having a prior relationship?
Yuu confessing in a moment of panic was like him deciding he'd make a last-minute effort to pass super hard high school entrance exams in a one-sided attempt to get Hikari to notice him.
He did it out of desperation thinking only of his own situation, with no real prep on his part, and both times it blew up in his face. But instead of pushing through and trying something different, he just gives up and runs.
And that's what I mean. He's been in love witu Hikari since at least partway through middle school. But he was forever passive and self-deprecating and relegating himself to the sidelines by labeling himself "unworthy".
If he's going to make half-hearted attempts and then simply bail without pushing through, then his growth potential as a character is very much in danger of stagnating, because he's just repeating the same pattern of behavior.