Can I advise you to stop apologising. You have said sorry. He's ignored you. You've said it again, and he's still ignoring you. So he knows you are sorry. If he is a decent person, he will be aware of your apology, and he will let you know that. If he isn't a decent person - and is deliberately punishing you by ignoring you - then he doesn't deserve any more apologies.
I could be wrong, and it could be that issue B is so dreadfully awful that he is totally consumed by that, but it reads as though he is punishing you for mentioning something he did wrong.
It reads as though this is all one way - you making all the effort / doing all the apoligising and all the supporting. He's ignoring you and making you feel bad, and ignoring what he did wrong. He is sweeping issue A (and your feelings) under the carpet to be ignored. He's ignoring you because you pointed out he was at fault and he's now deflecting to take attention away from that and make you the bad guy. He hopes you'll shut up about issue A and never mention it again. If you try to, he'll find another reason to ignore you until you learn the lesson (which is to never question or criticise him).
As I said, I realise I could be unfair as I don't know the circumstances, but in a loving relationship you don't ignore the other person / refuse to speak to them / refuse to consider an apology / leave them feeling bad deliberately.
And then there's the thing he did wrong in the first place. Don't overlook that. You may want to park it up while he deals with issue B, but it's still important that you have a full discussion and (if appropriate) you receive an apology from him, the same way you're happy to apologise to him.