«Since I left you, mine eye is in my mind;
And that which governs me to go about».
More from a sense of duty than a meaningful expression of emotion, the poet professes to see the young man in everything while he is away from the youth.
Since I left you, mine eye is in my mind;
The eye-mind dichotomy presented in the first line — “Since I left you, mine eye is in my mind” — recalls earlier sonnets in which thoughts of the young man contented the poet during their separation. Additionally, the use of the words “most” and “true” in the rhyming couplet is similar to their use in Sonnet 110 and hints that the poet is still trying to prove — perhaps more to himself than to the young man — his re-energized love for the youth: “Incapable of more, replete with you, / My most true mind thus maketh mine eye untrue.” Here, “most true mind” means that the only truth that the poet recognizes is his complete devotion to the young man.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com