Mr W.H was the person to whom Shakespeare dedicated his sonnets. In the dedication Shakespeare wished him all happiness and promised him imortality. Shakespeare released his sonnets in 1609 at this Stage Henry Wriothesley was a married man with three children and actively involved in buisness ventures. The release of the suggestive sonnets specifically adressed to Wriothesley would have been damaging to his reputation . Shakespeare knew this and was discrete , he used poetic shadowing in the dedication and reversed Wriothesley's initials and did not adress him directly as an earl.
Shakespeare promised Southampton imortality and with the sonnets he delivered.
The fact that Henry Wriothesleys initials have been reversed is an allusion to a mirror reversal of letters .
Shakespeare by his own admission loved to hold a mirror up to nature.
In this instance he is holding the mirror up to the Fair Youth.
The sonnets represent the immortal reflection of the Fair Youth . Wriothesley would grow old and eventually die but he would remain ever young and immortal within the sonnets .This is exactly what Shakespeare promises.
The fact that a mirror image is suggested in combination with the Fair Youth is an allusion to Narcissus. Narcissus was a character that Henry Wriothesley was openly compared to during his lifetime.