Your boyfriend would need to apply for a tourist visa (B-2 visa). He would start the process by completing a DS-160 online. Your boyfriend will need to show his intent to come for a brief visit. This is typically done by showing strong ties to the applicant's native country. He will not be issued the visa if the consular official suspects he is intending to immigrate.
Answered on Nov 30th, 2015 at 4:44 AM