Ok - constructive advice it is.
A COA doesn't convey permission to remain. A COA just allows you to marry. Even if you marry - as an illegal he will need to return home to apply for a spouse visa. He will not be able to apply in country for the 'easy' option of the spouse visa.
However, given he has entered with fake documents, and (presumably) been working, this may well result in refusal under 320 (11) (see
here)- which is basically a discretionary catch all 'has the person been frustrating the immigration rules'.
The fact that he's been issued with a deportation order isn't good either - it will only compound further problems.
My advice - he leaves under his own steam - not under UKBA's assistance - that'll make matters worse. You legally marry in Pakistan and hope that the spouse visa will be approved. If you take this route - you should be prepared to go to Pakistan to live.
The only other options I can see would be a discretionary leave application (which takes a long time and is by no means guaranteed to succeed) or an article 8 application - but I don't think there's a case for that here as your life could take place in Pakistan.
M.