Aito didn't know that those two years he thought he missed, were the most horrible years in his entire life.
He missed his friends. He missed Sakura, Yua and Haruto. He missed talking to them. He missed hanging out with them. He missed all the crazy things they used to do. What hurt Aito the most was that they were just in their first year of high school. They were yet to throw awesome parties. They hadn't even had their first taste of alcohol nor sex. They had so many plans. So many new things they wanted to try.
It took a long time for him to accept their deaths and Haruto's disappearance. In fact, he wasn't told anything until the doctors confirmed that he was ready to know. He couldn't believe it at first but later on, he slowly accepted it.
Life was short and the death of his friends proved it. It further strengthened his decision to live a happy life and not dwell on the past. What was the use anyway? None of them would come back.