Is it possible for my coworker to forgive me?

I work on a team of three people. We are all pretty close, but someones, one of the team members gets on my nerves. He is a nice guy, but he is not the sharpest tool in the shed. We always have to go over things again and again with him before he gets it. Yesterday, I instant messaged the third team member and said, "He is getting on my nerves, he is such a moron." Turns out, I sent it to the wrong person. (I know, that makes me the moron.) Anyway, now my team member is really upset and says I have broken the team. He said he will be cordial and professional, but he doesn't want to deal with me on a personal basis. Is there anyway to fix this major flub?