If you are not engaged, a fiance visa is not possible. Moreover you must meet in person first to file a fiance visa. He can try to get a tourist visa, but there is certainly a danger of refusal inherent in this type of request. You could also meet him in person first, and then decide if you want to marry him or petition him as a fiance.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
I agree with my colleague--However, you may waive the requirement of the in person meeting in the past two years. I suggest meeting with an immigration attorney as I know Pakistani traditional relationships do not support and frown upon "dating" prior to engagement and marriage.
If you haven't met face-to-face, you can't apply for the fiance visa.
A tourist visa is nearly impossible to get in this type of situation.
Have you considered going to meet him? If you do go, you might want to marry him there and then come back to the US to file more papers.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.