Since Sarah had left, Sherlock had gotten more upset, but happier at the same time. I know, it's confusing right? Let me explain:

He had gotten happier because, as asked, he asked Molly out. It was perfect. The only problem was, was that he hadn't told her that Sarah asked him to do it. Neither had he told her that he texted her every single day. Other than that, His life with Molly was great. They went on dates every other week. They had been going out for almost a year, you know, when it happened.

Nobody knew, not even Sherlock himself knew at times, but he was in fact, sad, he was the saddest he'd been in a long time. He was on the verge of having a knew best friend other than John, and at the very beginning of there friendship, she left. Just like that, he lost her.

He didn't know he was upset, in fact, it had to be pointed out to him. That day, was the start of a new adventure. True, it did break friendships and relationships, but that's life. Anyway, the relationships it broke, made way for better and stronger ones to take it's place.

This was the day Sherlock started finding the real him.

This was the day he started a brand new adventure

A new chapter,

This was the day Sherlock Holmes found out that Sarah White was missing.