At 25 years old Sherlock Holmes was old for an unmarried Omega. That he remained a bachelor despite being handsome, fiendishly cleaver and from both good breeding and great wealth was largely due lady fortune and a difficult temperament.
Unlike other well to do Omegas Sherlock had not debuted into society at the tender age of 17 owing to unfortunate circumstance, namely the sudden and devastating death of his mother two weeks before his debutant ball. His mother's death hit the family significantly hard resulting in them entering a deep state of mourning for a period of several years.
A good son would probably have concerned himself with his aged father's welfare during this time. Sherlock however devoted himself to his studies. It is during this period that Sherlock does what few Omegas manage to accomplish and finishes his education without a proverbial bun in the oven.
The formal mourning period while long eventually ends when Sherlock is 19 and shortly after a ball is arranged in his honour. All the local eligible bachelors of standing are invited as expected. Sherlock does not attend this ball however, as a few days before hand he accidentally upturns his small rowing boat while collecting water samples from the lake and falls into the shallow icy water. Being a strong swimmer he manages to make it back to shore safely, however by the time he returns to the main house he's caught hypothermia and a serious chest infection. More importantly his experiment is completely ruined. It takes him months to fully recover and even longer for his father to let him explore the grounds unattended.
Unable to delay debuting forever Sherlock finally gives in to his older brother Mycroft's demands and attends his aunt the countess of Cork's summer ball at the age of 21. He is unsurprisingly one of the oldest Omegas there.
He makes it through one dismal dance with a hideously rich passive aggressive beta with internalized misogyny and a serious victim complex called Sebastian who is nearly twice his age and who treads on his toes until Sherlock succumbs to food poisoning caused by bad shellfish and throws up on Sebastian's shoes. His father takes him home before he can cause any significant embarrassment yet strangely enough Sherlock is never pressed upon to attend another ball throughout the season, though his brothers Mycroft and Sherrinford attend them quite regularly on the lookout for an Omega of their own.
Shortly before his birthday and the start of yet another season, Sherlock's father suggests he come with him on his book tour across Europe. Sherlock accepts, glad for an excuse to miss the season and delay himself becoming bound to some brute of an Alpha or arrogant Beta looking only for meek and fertile Omega to bear them an Amanda of children.
The trip itself is wonderful and together they tour some of the finest museums and art galleries across Europe. Sherlock of course soaks up the culture like cats do sunshine on a warm day.
The only blight on their otherwise enjoyable trip is Sherlock's zealous suitors who flock to him despite his best efforts to dissuade and evade them, for as much as he is loath to marry the thought of living on some foreign shore is unbearable. Thankfully his father shares his sentiments and turns down each and every one of his son's foreign suitors and so despite the efforts of the majority of Europe and a particularly feisty American by the name of Miss Adler Sherlock returns to England single.
Winter changes to spring and Sherrinford acquires a mate called Victor. Sherlock and he take to each other quite well, being the only Omegas in the household.
Or at least they do until Victor starts to swell with child after child and glow with such blatant happiness that the entire village are either jealous of his brother's good fortune or Victor's abundant fertility. Sherlock refuses to assist with the children as much as possible and retreats further into his laboratory claiming children to be a bore and a waste of his time.
In reality he is slightly envious, himself unable to be with his beloved Johnny. As much as everyone believes love to be a mystery to Sherlock they are wrong for he understands all too well having lost his heart to a young soldier in his youth. Johnny is secretly the reason he is loath to marry anyone, for he is Sherlock's soul bonded not that anyone besides his Johnny is aware of this.
Johnny fair and short had spent almost an entire month as a guest at the Holmes's large estate with his professor Mike Stamford a friend of his father's when Sherlock was merely a boy of 15. Mycroft had been away at university and Sherrinford busy working in London so it had been just the two of them taking walks in the orchards and reading in the library. Johnny, though slightly older treated him like an equal in all sense of the word and a gentleman throughout their association (unlike Miss Adler who had tried to trick him into showing her his mark and attempted to copulate with him while he was in a drugged state).
Johnny had thought him brilliant and together they discussed almost everything, from chemistry to astrology. Johnny's kind smile and warm heart had made him terribly easy for Sherlock to fall in love with. That Johnny had turned out to be the one to match his soul mark was amazingly wonderful. What was not wonderful was the hopelessness of their relationship.
With Johnny being from neither from a distinguished family nor particularly wealthy any sort of match had been impossible at the time of their first meeting, given his mother's ambitious desire to use Sherlock as a way of climbing the social ladder. With a heavy heart Sherlock had said goodbye and watched Johnny go off to fight a war knowing he was unlikely to ever return.
At 25 Sherlock sole comfort is the knowledge that his father has not the need nor want to marry him off and is instead perfectly content to have Sherlock remain at his side as his chess opponent and main source of entertainment (father was particularly fond of violin performances even when they were impromptu and given at three in the morning).
The day Mycroft returns from London and informs father he has found Sherlock a husband is a very distressing day indeed.
By the time Sherlock finds out about it of course there is nothing to be done, for his father has already met the man who was to be Sherlock's captor and signed the required paperwork.
Despite this Sherlock tries to reason with his usually sensible papa. His father having been brain washed by his swine of a brother simply tells him not to worry and that it is a wonderful match and that his intended was a wonderful man who had saved his brother life.
The brief surge of joy Sherlock feels upon learning his brother owes someone a debt of gratitude in exchange for saving his life and rescuing him from an alleged assassination attempt is quickly quashed upon realising that he has been used as a means of absolving this debt.
Sherlock decides then and there that he hated his husband to be, one Dr Watson. There was no way he could like a man who had assisted his arch enemy after all.