Uhm, if he doesn't talk to you or try to apologize to you about it. Would it matter if he stayed on your FB and MySpace. I mean, it's weird how people look at things. I'm black, I call my friends "Niggas" not "Niggers" but some say it means the same thing. I believe "Niggers" has a more emotional compassion and realism behind it.
Dogs don't like Cats, so when a Cat sees teeth in a Dog it runs for the nearest tree. What I'm saying is, you could of just as easily called him a stupid cracker if you wanted too. We all try to hurt other people when we feel threaten or hurt over selves.
Example, if you and I were dating and we had the same argument that you had with your boyfriend, I would have called you a "Nigger" because I'm black myself, would only be contradicting my self in that sense. I'd probably use a slightly same meaning, "Your Ignorant" or "Stupid." Or maybe I'd bring up some random girl I could have dated instead of you.
However, it was nice or at all appropriate that he called you a "Nigga/Nigger" so therefore, delete if you wish. You don't have to explain yourself either, you've already told him how much you dislike it.
For the record, my white friend has called me a "nigger" once, and I actually went along with it. I tried to push some buttons to see how far he would go with his statement. I didn't think he actually meant it, I just felt like he felt threaten and wanted to hurt me, the deeper the lies, the further it cuts like a sword. He didn't have much on me, since we were but mutual friends, so he resorted to the only thing he could think of.
But again, doesn't make it right, especially in the sense that he's your boyfriend (or was) and his job is solely to protect your best interest.