Well, said friend appeared on Facebook, and I figured I'd try one last ditch effort to try to make nice. I got a response while I was out of town which says, in effect, "Dude, no. I'm done with you. I was done with you four and a half years ago. Please, move on."
Strangely, I'm okay with this. If nothing else, it gives me a finality that had been missing (but admittedly implied) the last 4 years. And it lets me close the chapter knowing that I apologized every chance I could get and did everything I could to try to resolve things, but there's only so much I can do without any effort from the other party. If my apologies and attempts at reconciliation aren't enough, then there's nothing more I can do. So finally, I'm able to tell myself that I can move on, and that it's OK to move on without beating myself up about this crap anymore.
In other non-psychobabble news, I'm back from Chicago, and I had lots of fun seeing old friends.