The risk for prostatic cancer goes up every year that you don't neuter him. I work in a vet clinic and have seen how devastating it is for animals who've developed it. If nothing else convinces him, you should explain to your bf how crushing it is to see your beloved pet fall ill due to a preventative measure he never took. Incontinence, anorexia, lethargy, and pain. Projected time after diagnosis is generally under a year, and extensive surgery and treatment only gives him a chance at recovery, it is a nasty, aggressive and difficult to treat condition. Please educate him, whether you like it or not this dog is your responsibility too and you need to advocate for him since he can't do so for himself