“thy image should keep open”
'Image' here does not mean a painted or carved likeness; it means the mental apparition — the inward picture of the beloved that the poet cannot banish from his mind. The poet asks whether the youth is deliberately making his own image haunt the poet's sleepless nights.
“shadows like to thee do mock my sight”
'Shadows' means insubstantial phantoms or likenesses — not cast shadows but false semblances that look like the beloved but are not him. 'Mock my sight' means deceive or delude my eyes. The poet lies awake and sees the beloved's face everywhere, in shapes that counterfeit him but vanish.
“The scope and tenure of thy jealousy”
'Tenure' is a legal term for the terms or conditions under which something is held — here, the full terms and extent of the youth's jealous surveillance. 'Jealousy' in this period meant watchful suspicion or zealous guarding, not simply the emotion of romantic envy. The poet imagines the youth sending his spirit to pry into the poet's 'shames and idle hours' — the scope (reach) and tenure (terms) of that spying mission.
- TLN 852historical topical
“To play the watchman ever for thy sake”
A watchman was a parish or ward officer who walked the streets through the night, keeping guard against fire and crime. The poet transforms his sleepless love into the same kind of vigilant, duty-bound service — not passive suffering but an active watch kept on the beloved's behalf. The word 'play' acknowledges the role is performed as well as felt.