The speaker uses an extended, slightly sarcastic comparison to express his hurt. He says his beloved is like the careless heir of a miser: after the old man dies, the son inherits a fortune but has no idea how to value it. He throws money around wildly—partying, buying friends, wasting it on anyone—except for a tiny loan he happens to give one honest man. In the same way, the speaker says, you squander your gifts. Your beauty fades with age, your kindness is spent on false friends who will deceive you, your love lands on unworthy people. And what did I get? Just that “little which to me was lent,” a small, almost accidental sliver of your attention.
The final couplet delivers a cool, quiet payback. Once all the rest of your beauty and love is gone, the speaker says, I’ll give that borrowed morsel back to you. It’s not a moment of generosity—it’s bitter satisfaction. The mood is one of knowing resentment, spoken by someone who’s been sidelined but watches with a kind of grim clarity as the beloved’s riches run dry.