I had the same problem. I've finished the game, and I'd say he's the hardest boss. Took me ages.
My tips for beating him would be to be patient when countering. If you press triangle too quick the counter will fail. That was my problem. If you wait then you should be able to see the opening to counter. I don't know exactly where you're going wrong, but I found that as long as you get the counter right he can't damage you. Then all you have to do is attack.