Unfortunately it sounds like it's going to be too late for him to get an accurate lesion culture and typing - they are best if done within 48 hours of the appearance of the lesions
When he sees his doctor he should ask for a type specific herpes igg blood test to see what his status is ( don't bother with the igm - it's worthless ). You also will need to get a type specific herpes igg blood test to see what your status is too so that the two of you can make informed decisions about what precautions to take, if any.
Did he have to have cheated for this to just now be showing up? Not at all!!! He could've had genital herpes since before he met you and he's just now having his first obvious recurrence that was obvious enough to make him take notice or you could've had it since before you met him and just recently transmitted it to him even though you didn't seem to notice any symptoms. Also you can transmit hsv1 from the oral area to the genital area thru oral sex too . Until you figure out who has what - be sure to take precautions against transmission - just in case you are negative for whatever type he has.
The herpes handbook at www.westoverheights.com
and also the info here at asha is terrific to help you learn more about herpes. Both of you should be sure to read them both when you have the time.
Let us know if we can help you with your test results or anything else you need