Unfortunately, we don't have same sex transmission stats. We know, generally speaking, that men who have sex with men, have higher rates of STD transmission than any other group, but exactly how much higher the transmission is for herpes, we don't know.
Assuming you're using lube and condoms, it's probably not that much higher than male-to-female transmission, which we do know.
The transmission rates for hsv2, male to female, over the course of a year, assuming sex 2-3 times a week:
Only avoiding sex during an outbreak - 8-10%
Adding condoms OR daily suppression - 4-5%
Adding condoms AND daily suppression - 2-3%
Is there a specific reason he doesn't want to take antivirals? Anything I can help with there?
I'm glad you've found someone you really like. :)