S. R. Faruqi:

Contractedness, silence, and constraint are the qualities of a bud. Then, a bud that has been broken off from the branch very long ago will have already withered as well. Because of the contractedness, etc., of the heart, it's also used as a simile for the heart.

We hoped for faithfulness from the beloved; when she showed faithfulness, then the bud of the heart would have opened out. She never showed faithfulness at all; and while waiting, we were drying out, until we became like a bud that had been broken off from the branch very long ago-- that is, we already had a contracted heart and constrained lips, now we became withered as well.

A dried-out bud is of no use; it has neither color nor scent. Its fate is to be cast away. The simile is extremely eloquent [badii((], and the causes of similitude are multi-layered.

FWP:

SETS
MOTIFS
NAMES
TERMS == SIMILE

SRF takes der-chiidah to mean 'long ago broken off from the branch', so that its basic sense here would be 'withered', and that certainly works well. But there can be more possibilities. In Persian, chiidan means 'To gather, collect; to select, pick, choose' (Steingass p.405); these senses are also found for chiidah in Platts (see the definition above). And each of them yields new 'causes of similitude'.

If the bud was 'gathered', then that means the beloved had perhaps selected it out for future use: she would put it in water till it bloomed, or include it in a vase to accompany some full-blown flowers. But the bud was 'gathered' long ago, and since then the fickle beloved has apparently left it lying in some niche and ignored it.

If the bud was 'picked', that's a neutral description. Children pick flowers sometimes for no reason at all. People pick flowers and sometimes treasure them, sometimes forget about them, sometimes toss them away. As we know, the beloved is capable of anything.

If the bud was 'culled', then it might have had an even darker fate: it was perhaps weeded out, discarded, 'rejected because of inferior quality' (a common meaning of 'culled'). Of course, Platts might not have intended the negative sense of 'culled', since the other English synonyms he chooses are all positive; but it's worth considering.

Thus chiidah might suggest not merely a state of being 'withered', but also a more active commentary on the beloved's treatment of the 'bud' of the poor doomed lover's heart.