Kab Se Hunn kya bataoon

Qaasid ke aate aate hi khat ik aur likh rakhuun
main jaanataa huun jo vo likhenge jawaab mein

Let me write a letter before the Postman comes back with the message from my beloved as I know what the reply is going to be (or there will be no reply). Please appreciate Ghalib's humour here.

[Qaasid : Messenger]

kab se huun kyaa bataauun jahaan-e-kharaab mein
shab haaye hijr ko bhii rakhuun gar hisaab mein   

Since long I have been in a world of problems if I include the nights and the period of separation. 

[Jahaan-e-kharaab : World of problems; Shab : night; Haaye : shame; Hijr : separation ]

mujh tak kab un kii bazm mein aataa thaa daur-e-jaam
saaqii ne kuchh milaa na diyaa ho sharaab mein  

When did it happen in her party that I got a chance to have a glass of liquor when it was served among the guests (There was always none left till the tray reached me). And today that I am getting a oppurtunity to have a glass that I am suspecting that the bar tender has mixed something in the liquor. This has a literal and implied meaning. Please try and understand both. 

[bazm : mehfil; saaqi : bar tender]

taa phir na intazaar mein niind aaye umr bhar
aane kaa ahad kar gaye aaye jo Khwaab mein

It may happen that I may not be able to sleep throughout my life as she came in my dreams and promised me to come and meet me.

Ghalib chutii sharaab par ab bhii kabhii kabhii
piitaa huun roz-e-abr-o-shab-e-maahataab mein

I have left alcohol but I stlll drink sometimes on cloudy days and moonlit nights.