Sherlock is not the type to indulge in romance, and is more attracted to intelligence than anything else. His only real canonical love interest is Irene Adler, because she manages to outsmart him and is generally fascinating in that regard. But then she betrays him and he ruins her plans and then he saves her from getting beheaded by terrorists. LONG STORY SHORT she's dead to everyone but him and they can't see each other again unless they want to risk her safety.

BUT NOW she's in the City and he's trying to deal with the ~emotions she brings out again. She's probably stolen a kiss from him on New Year's, but other than that, he's really not up to anything in this department.

Fandom-wise, people love to pair Sherlock with John but I could not disagree more with that. I can only see them as best friends/surrogate brothers that warm my heart and give me fuzzies.