There is no reason to be puzzled here.
It can be that your boyfriend too may be having an acute UTI.
My advice for you would be that both your partner and you should practice safe sex
, i.e. use condom every time while having the intercourse. Both of you should maintain good personal hygiene. Drink plenty of water.
A single dose of azithromycin
should help him. It is a prescription drug. Get it prescribed from a physician.
You both should be fine soon.