Nasir was a twentieth century poet who was born in undivided India and then emigrated to Pakistan when the countries were split in 1947. There is a version of this song sung by Asha Bhosle and Ghulam Ali in Meraj-e-Ghazal which was one of most favorite albums growing up. The original version was by Noor Jehan, I think.

“Haal-e-dil hum bhi sunaatey lekin
Jab wo rukhsat huye, tab yaad aaya
…
Dil dhadakne ka sabab yaad aaya
Wo teri yaad thi ab yaad aaya”

Roughly translated…

I, too, would have told her about my feelings for her
But I remembered about it only after she had left
…
I suddenly realized why my heart still beats
It is for all the memories that I have of you. Now I remember.