Before becoming a US citizen or even being eligible to become one, one must be a US permanent resident (green card holder) for the requisite period of time.  If you are planning to go meet each other in person and see where it takes you, that's an excellent idea.  If after your meeting you decide to proceed with engagement and marriage, you can file a fiance visa petition on his behalf and once that's approved, he would be issued a fiance visa which would allow him to enter the US for 90 days to get married to you.  Once you are married, you can petition for him to become a permanent resident (green card).  Please let me know if you have any additional questions or how I can be of further assistance.