Assonance gives the poem musicality, linking words together and bringing metaphors and images to life.
In line 17, for instance, the long /i/ that travels through the words "my bridegroom and I" emphasizes the new connection between the speaker and her new husband. At first, that might seem romantic. But the continuation of the same assonance through the next few lines suggests the speaker feels pretty ambivalent about her marriage:
Our eyes changed colour
like traffic-lights, so they said.
The time was not ripe
for us to view each other.
The speaker and her husband might be connected, but they're certainly not seeing "eye" to "eye" just yet.
Later, they have to confront that fact head-on:
we turned and faced each other
with turbulence
and imprints like maps on our hands.
The guttural /tur/ sounds of "turned" and "turbulence" suggests how difficult the couple's connection feels. But the gentle /a/ of the "maps" on their "hands" also suggests that, with work, they might find their way to an easier understanding.
Assonance also appears in the speaker's lost dream of a happier (and emphatically Pakistani) wedding:
I wanted to marry a country
take up a river for a veil sing
in the Jinnah Gardens
That repeated /ih/ sound gives this wistful vision its music.