If you are wrong ...then apologise and hope he comes round, if he is in the wrong ask him if this issue is a symptom of something bigger going on. Is there a deeper reason, is he trying to make you feel bad because he feels inadequate and trying to regain power in the relationship? Is he having an affair and feels guilty so trying to make it seem like you are not getting on so you make it easier for him to go, lots of possibilities, but if you get him to open up be prepared for things you may not wish to hear, even if it's only had stuff from before you knew him affecting his behaviour now.