This is a very, very common situation with new horses. I don't even want to call it a "problem" because it really isn't. Some horses just take awhile.
It took me about a year with Buster to build our bond. He was the dominant
horse on the farm and didn't really build relationships with any other horses, either. It discouraged me because I didn't want him to be aloof and refuse to come to me.
So here's what I did:
-I used treats judiciously. As long as he's polite, never puts his teeth on me, and respects my space, he gets quite a few carrots and Manna Pro Apple Wafers. That helped a lot.
-Here's the second part and one that a lot of people overlook. A horse has to have a reason besides just the food to want to bond with a person. The horse needs to respect the human as a capable leader. This comes through training, especially ground work. I follow Clinton Anderson, but all good trainers have somewhat-similar methods.
Once Buster realized that I was a capable leader and I expected him to follow my leadership
, our bond started to deepen.
Now, Buster calls to me as soon as he sees my car arrive at the farm. He'll also cross a huge pasture to come see me if he hear's me call his name.