Ugh. That didn't take too long at all. I'm sorry, dear. *BIG HUGS*
I don't think this is anyone's fault. It's just incompatibility. One day, you may be in a position where you must let someone down gently... and it will be gentle because you know how it feels. For him, there might still be some karma waiting in the wings if he's not careful. I don't know the exact details there.
Either way, this is a shitty situation. I wish there was something I could say that would make all this ugly business go away, but I've been heartbroken a few times myself. I know there isn't anything that will help other than time, patience, and different outlets and opportunities to express your grief.
I don't think him showing you that he's hurting too would be of much help. When we're down in the dumps like this, we tend to look at things like that and find hope where there isn't any... and hope can be incredibly misleading and delay our healing. I think it's a blessing in disguise that he's not showing you any remorse and moving on. It hurts, but the hurt will make it easier in the long run.
And honestly, I know this thread has been about looking at things in balance and shades of greys, but it is ok if you need to move into looking at things in black and white terms for a while. It simplifies the feelings and makes them easier to digest. And its therapeutic. Sometimes we have to move to extremes to find our middle, so hate him now, if you must. Get as angry as possible. Make him loathsome and disgusting and shut him out. It's OK to do that. You're just purging feelings. Be livid. Be sad. Be whatever it is that you feel. It's part of the process... you'll be OK eventually, I promise.
In the meantime, if you need us, we're here.