“we two must be twain, Although our undivided loves are one”
'Twain' means two; separate. The speaker opens with a deliberate paradox: their loves are one unified thing, yet they must live as two separate people. The whole sonnet unfolds from this contradiction between inner unity and outward division.
historical The sonnet form“those blots that do with me remain”
'Blots' are stains or marks of disgrace. The speaker deliberately leaves their nature unspecified — some unidentified misconduct or scandal of his own that, if publicly associated with the Youth, would damage the Youth's standing. The vagueness is intentional and private.
“In our two loves there is but one respect, Though in our lives a separable spite”
'Respect' here means concern, regard, or quality — the love they share is of one nature. 'Separable spite' means the cruel force (whether fate, circumstance, or the speaker's own disgrace) that compels them to live apart. 'Spite' carried the older sense of harm inflicted by fortune, not merely personal malice.
- TLN 499historical topical
“I may not evermore acknowledge thee, Lest my bewailed guilt should do thee shame”
The speaker cannot publicly greet or claim the Youth because his own shameful reputation would, by association, damage the Youth's standing. In Elizabethan society reputation was managed through the company one kept; to be publicly connected to a disgraced person was itself dishonoring. This is the social mechanism that enforces the separation announced at the sonnet's opening.
historical The Fair Youth, the Dark Lady, and the Rival Poet