My partner wants to live in the U.S. with me now he can only visit every 6 months on a visitors visa

The best approach in this situation is to apply for a fiance visa (K1) and your partner can travel to the US specifically to get married to you (the marriage has to occur within 90 days of his entry on the K1 visa).  He would then apply to adjust his status to that of a permanent resident.  I would not recommend marrying outside the US and then trying to bring him here on an immigrant visa.