My wife is going through the immigration process to the US, and I am a US citizen. Once someone from another country marries a US citizen they become ineligible for a travel visa to come into the US. If you got married to him while he was visiting the country by travel visa, once his travel visa expires in order to comply with US law he will have to go back to Pakistan and stay there until you complete all of the required citizenship paperwork/process which will take at least a year, possibly 2 years or more to complete. If he overstays his visa and doesn't go back to Pakistan, it is very likely that they will not give him citizenship since he broke US law. They will consider him an illegal immigrant.