I was dreaded the whole chapter that Hikari will sweep everything under the rug just like that. That's a good build up for the twist on author part, especially for all the bullshit Hikari has ever endured before, it's not too unthinkable she'll accept this one, too. Good thing it concluded this way. Rip the bandage now rather than keep it on and let he wound fester deeper. Clear everything up, and decide which direction all of you want to go next.
As for Yuu, not to say what he did was correct, but it was understandable. The whole thing with Ayami is something he knows full well will get ugly if Hikari ever finds out; so, in the circumstance he thinks he can get away with it, it's only human to try to hide it; confronting with one's own false in never easy. However, in not doing so, you will eventually have to confront its consequence one way or another. It can be a direct consequence just like this, or a long and failing relationship of distrust if everything is kept under wrap.
Lesson here, kid? Come clean as soon as you can.
Unless you think you'll never see the person ever again in this life (which doesn't mean it's a good thing to do, just less consequence and I'm not one to judge you on that), the longer you hide it, the more consequence you'll have to face one day. And consequence can come to you in a round about way, too. Maybe no one ever finds out about the lie, but one day you might have to accept something unpleasant just to keep your lie straight -- that's also another form of consequence. And it can pile up the longer you keep it. Trust this old man and don't thread the path he did.
