Mmm, that's one sexy high-schooler.
On a more serious note, to the people complaining about a lack of sex, don't forget that Yuya is still a teenager traumatized by his parents abandoning him, giving him severe low self-esteem and trust issues.
Yes, he's gotten a lot better thanks to his loving girlfriend and close friends, but he's definitely still got thoughts like "Am I really good enough for her?, Do I really deserve to be this happy?".
That stuff doesn't magically disappear as soon as you let some happiness back into your life.