Your horse is bored! Do not just come to him to ride, you should hang out with him and have fun. When you are not there he should be turned out with one of his horsey friends a lot and go to his stall at night or during feeding time. Also don’t always ride him in an arena; try riding him in other places or just go riding for fun like trail riding. All in all, if you play/hang out with him he will forget all of his bad habits and learn that your are a trust worthy friend.