How are his training sessions? Are they fun for him? My TB taught me a lot about his enthusiasm level being contingent upon the previous days work. ;) When I first got him, he would walk away from me if he saw me coming with a halter. A few months in, he would walk up to me instead. But I did notice that if we had a stressful training period the day before, if I got short tempered with him or it didn't end on a good note, the next day he might walk away again or stop on his way to the arena, etc. I started keeping all of our training very positive. (Not EASY, but always positive. Like, he walks away thinking that he is the most amazing horse in the world, I make a big fuss over him when he gets the right answers.) Now, it's a game. He wants to be a good boy. He is the first one down at the barn every morning, volunteering for his morning tasks! Just a thought.
~And He created the horse and said to it, "I have made thee without equal."~