I didn't tell him that I was promising him that I would always stay in touch. I knew that he wouldn't believe me, and it would only lead to (another) argument.
Nine years later, we've been mistaken for dating, mistaken for married, been through all kinds of hell together, are a lot saner, a lot sillier, and get along a lot better. I finally told him, I think last year. There have been times when I've been tempted to just walk away -- we're both human, and I don't deal with conflict at all well -- but I care about him, and I promised, and somewhere underneath all the sarcastic bastard, he enjoys my company as well. I'm here, and he's there, and despite all the things that could have gone wrong, we're still friends. Never going to say goodbye.