I just went through the same thing with my male GBR...right after breeding he seemed to get these white pimple things on his forhead...they got bigger and started to break open and looked very nasty. I dosed the tank with Ich rid, Metro, Meth blue and Binox to see if any of these things would stop the erosion that seemed to be eating at my lovely boys head.
During this time the female never got anything wrong with her, and they even laid more eggs which he fertilized too, to all outside appearances he was just fine.
I noticed he was starting to get a bit bloated looking and not eating as much as normal, even though he was still guarding his eggs etc.
Then one morning I turned on the lights and he had passed away during the night....I was soooo upset. I had tried everything to keep him alive, but all for nothing.
I read somewhere it happens to rams from stress from breeding/or breeding stress, but the long term outcome is not good. I am not trying to frighten you, but you need to be prepared for the inevitable loss of your fish to circumstances that we just do not know the reasons for....and no matter what we do it will not make any difference.
I hope this doesn't happen for you, but I am forewarning you that it may be the same as my fish.
Soooo very sorry. I wish I had a cure for it.