S. R. Faruqi:

In dil-pareshānī there's a 'reversed izafat' [iẓāfat-e maqlūbī]-- that is, pareshānī-e dil . A 'reversed izafat' always raises the rank of a verse, because there's eloquence [badāʿat] in it. Then, dil and gul , because of their redness, have an affinity. And rang too is excellent, because of the wordplay with gul .

But it's also possible that dil-pareshānī there might not be assumed to be an izafat. If we read it with an izafat, then the prose will be dil kī pareshānī mujhe gul ke rang bikhere detī hai . If we assume it to be without an izafat, then the prose will be dil mujhe pareshānī de hai , aur gul ke rang bikhere hai . That is, in both cases, in the speaker's personality and life there's a dispersion/confusion. The difference is that in the second case the cause of this dispersion is his own heart, and in the first case the anxiety of the heart is a general situation-- its cause can be the beloved, or the world, or something else.

Now please look at the second line. A bud is called an afflicted/'imprisoned' heart. The anxiety of the heart that is scattering/disordering the speaker-- instead of that, a heart-collectedness like that of a bud is desired. But this heart-collectedness too-- of what use is it, when its meaning is the affliction/'imprisonment' and silence and melancholy?

Then, the word āh in the middle of the line is endlessly meaningful, because through sighing the heart becomes even more defeated and broken to pieces (because of weakness, or because of the effects of the sighs, etc.). Thus the thing that he wants to decrease (the anxiety of the heart)-- his act of sighing is causing it to increase.

Then, consider also that the bud finally becomes a flower and blooms, and then in any case is scattered/disheveled. Thus even if he would become unified/collected like a bud, what of it? Either he'll be destined to heart-affliction and melancholy, or he'll have to bloom and become scattered once more.

There's also the point that the heart and the rose have an affinity because of their redness-- and also because the heart too, like the rose, is being scattered out in pieces. But with regard to affliction/imprisonment and aspect, there's also an affinity between the heart and the bud. That is, the heart in any case looks like a bud, and nevertheless it doesn't attain unity and collectedness. Now even if he would make himself collected like a bud, what good will it be?

FWP:

SETS == IZAFAT
MOTIFS
NAMES
TERMS == IZAFAT

The bud has composure and 'collectedness' [dil-jamʿī]-- but also 'narrowness, tightness' [tangī] and 'imprisonment' [giriftagī]. When it opens out into a rose, it smiles or laughs-- but then all too soon fades, and its petals become 'disordered' [pareshāñ] and 'scattered' [bikhre huʾe]. The central word here is pareshānī (see the definition above), with its range of meanings that potentially includes both the state of the 'narrow' bud (in the metaphorical sense of 'anxiety, distress'), and the state of the disordered, disintegrating rose (in the literal sense of 'dispersed, scattered').

The classical ghazal poets rework this theme many times in the course of their divans. As SRF observes, here the 'ah!' is particularly effective, since its melancholy suggests the no-way-out predicament of the heart that can only hope to resemble either a bud or a rose.

Here's Mir's best-- a version subtler and more allusively complex than the present one:

{6,2}.

The discussion of {6,2} includes a link to Ghalib's best treatment of the theme, with its unsurpassed and unsurpassable second line.