He heard the whispers, of course.
Even if he hadn't been a genius with the Holmes' powers of deduction, he would have still known.
Sherlock turned his attention back to the dissection he was working on, ignoring the group of 3 who were sitting at the table behind him and watching his every move.
"He's a junkie, you know?" one of them whispered. "I heard that he was in rehab before he came here."
"Once a junkie, always a junkie, I reckon." another replied.
Sherlock closed his eyes tightly for a moment, blocking out the sights and sounds around him. In his 18 months at university, he had so far successfully resisted all temptation but it hadn't been easy. He'd had to deliberately separate himself from his peers to avoid any situations where drugs might be freely available, and it had made him even more unpopular.
"Tell me about your friends, Sherlock." Mummy would say, her eyes bright and excited at Sherlock's new start in life. The children at school had been cruel, and university afforded him a second chance at making friends with his peers.
"They're all boring." Sherlock responded with a shrug. He couldn't explain, of course. He couldn't tell Mummy that he had no friends because he had distanced himself from everybody else. She didn't know about the drugs.
Even Mycroft kept on at him about how he needed to form alliances with his peers. He worried constantly and he couldn't imagine how Sherlock was coping alone.
His own brother didn't understand.
They would never understand how alone protected him.