As some one who needs to hear the apology BEFORE any explainations/ justifications, this is a HUGH deal. My husband is like you and thinks that his explanation and the intent behind is good enough. For someone who actually needs to hear the words "I'm sorry", this just comes off as a justification. Until there is a genuine apology with NO explanation/justification, those of us who need to hear it can't move past the hurt. Our brains can't shift gears beyond the hurt until we hear a genuine apology.
You claim to be sorry that you hurt Grotto, but can't bring your self to say it. To him that says, you don't really care about him and that he was hurt. Why is it hard to say, "I'm sorry my actions hurt you, that was never, my intent"? Apologizing for hurting him, is not admitting your actions were wrong. It's necessary to put out the fire before trying determine how it started in the first place. The embers are still smoldering, go put out the fire. Then tell him, your willing to try and find the real problem and work on a solution when he is ready.