Hi D, He may somehow in the not so past when engaging in sex with you, you could have been a bit dry, this would have put a strain on his p***s head skin and he ended up with this small tear, now the best thig for him to do is just wash it twice daily with a warm sea salt wash, this will help clean and heal his small wound, his problem is that each time he gets an erection it will open, so see if he can refrian from masturbating and sex for a coulple of weeks to see if it heals.
Good Luck
I would see if Lotrim cream helps. Next I would try aloe vera. I would change over to those new sports underwear that stops chafing and breathe well.