If I owned Sherlock™ I would just make their gayness canon already; the sexual tension and gay jokes are getting ridiculous.
Sherlock knows that John will be coming soon. It happens every night. Days belong to Sherlock, but the nights are all John's.
Sherlock doesn't mind because it keeps John with him.
Sherlock never has, nor ever will, care much for sex. Sex is messy, unhygienic. Sex is a motivation for those who Sherlock dedicates his time tracking down. Sex is a release that slows the mind. Sherlock hasn't time to care about sex.
Sex is different with John. Not because Sherlock magically finds himself interested in genitalia or the grunting release, but because Sherlock wants John around. And John wants sex. Sherlock wants all of John's time, meaning that Sherlock cannot have John spending it with other partners. So having sex with John is a fine compromise. Needs are met and John will always be there in the morning with tea and compliments. John will buy the milk, Sherlock will submit to John's sexual desires. All is fulfilled and none are left wanting.
So Sherlock waits. He is neither dreading nor eager; just waiting.
To keep John in the daytime is worth the nights of sticky human contact.