Sherlock didn't expect another visit by the DI, much less that he just wanted to see, if he was okay. This DI cared about him. That was strange. Nobody besides some members of his family ever cared about him, and he always had the feeling they cared out of a sense of obligation rather than because they were genuine concerned about his wellbeing. But this man cared. It was a puzzle and Sherlock loved puzzles. And when they started to talk the DI surprised Sherlock even more when he listened to his deductions and promised to act on them. People usually hated his deduction and didn't believe them.
Thus began the first real love of Sherlock's life – his work. Well, first he had to get clean, the DI made that quite clear when he offered to let Sherlock have a look at some cold cases. And he had to stay clean, which wasn't easy, but he made it, admittedly with the help of Mycroft and a rather posh and extremely boring rehab centre. But after that Lestrade asked him for help every now and then and he also encouraged him to start a website to gain some private clients. The older man wasn't his soulmate but he cared and he gave Sherlock a purpose.
It was months after Sherlock started to consult Lestrade that he found out the DI's first name. Lestrade was extremely annoying that day and so Sherlock stole his warrant card. It should have been just a joke. He really liked Lestrade and he had the impression that Lestrade like him as well. He offered him crime cases against the boredom. Sometimes he even brought him take-away and urged him to sleep. He cared so much for Sherlock's wellbeing that it was really a little bit creepy. But the man was undeniable the best that had ever happened to him. He even resisted Mycroft's attempts to bribe him to spy on Sherlock. So stealing the warrant card was supposed to be just a joke. When Sherlock took a look at the warrant card he felt how his heart skipped a beat. "Gregory." He slumped down on the sofa, starring at the name.
Sherlock stayed for hours in his mind palace to think about this new information. Lestrade cared for him, but he hasn't reacted on his name. He covered up his mark all the time, but Sherlock still hasn't found out the reason for that. He was strangely attached to Sherlock, but he hadn't made any move to ask Sherlock about his mark, even though Sherlock was sure that the DI had noticed the silver band that covered his wrist.
At the end Sherlock had this itchy feeling that Lestrade might be the one. He got up from the sofa and grabbed his violin. As a played through several pieces he came to a conclusion. He would never dare to be the one to make the first step. First of all, the social rules were quite clear. The healer needed to make the first move; it was not the right of the broken one to approach the healer even if you were sure that it was your soulmate. And even if Sherlock didn't care much for other social rules breaking this one could end in a disaster. If Greg was his soulmate and cared for the rules he could reject Sherlock's approach and could even reject the bond. And even if he didn't care for the rules, if Sherlock would be wrong with his assumption that could destroy the life he by now had build up for himself. Who would ask a broken one to consult on a crime scene? Prejudices were still strong. And even if that would be still the case Lestrade surly would see Sherlock differently, probably with pity and disgust.
Years past by. Sherlock tried to gather more data, but there was no way to confirm his assumption. In all those years he had absolutely no opportunity to see Lestrade's mark. And even though he still cared for Sherlock, he had never approached him to ask the one question. Sherlock came to the conclusion that either Lestrade hadn't a broken mark, or that this Gregory wasn't his Gregory or that Lestrade just didn't want to bond with him. It didn't really matter which conclusion was the right one, Sherlock couldn't change the outcome. Sherlock knew that the probability was in favor of the first two explanations, but somewhere deep down he thought that Greg didn't want to bond with him. He felt rejected once more, rejected by the one person who should accept him, even love him. A quite kind of desperation made a way into his heart and it would have surely ripped him apart over time, but then John entered Sherlock's life. Things changed. Now it was John who cared for Sherlock, accepted him and his way of living, he even tried to keep him fed and make him sleep enough. With that Lestrade seemed to feel less obliged to take care of Sherlock and it made Sherlock sad, but it also eased the pain. Maybe he wasn't his soulmate after all.