My new horse is getting bullied, how can I stop this?

I live on my parents farm, and I own 5 horses. I am extremely close to all of my horses, but my new horse is getting bullied by my dominant stallion. Before everyone goes and umes things, this is no ordinary stallion. He was my first horse, and he is a paint, but he has won many first places, and is a great all a round horse. I also have 2 QH mares, and a Welsh gelding. When ever I put them all in our large pasture, they act like best buddies. My stallion ( his name is Sammy) always have perfect manners, and never tries to kick or buck, or even get in fights with my Welsh gelding. I have been thinking about getting another horse, but have never found the right one. Recently, my trainer found friendly a 3 year old Icelandic horse. He was a gelding, and just what I was looking for. A few weeks after I bought him, he seemed right at home, and I introduced him to all of the horses, except Sammy. I got my trainer to help me with introducing my new horse to Sammy. Before we even got him by my new horse, it's like a bomb was set off right be side Sammy, and be just went crazy. I had to hold on with all my might so that he wouldn't run off. The next time I tried this, I took a little more precaution. But this time, It seemed as Sammy didn't even care that he was there. My trainer said it was okay that I put them all in the pasture, but I just had to watch them. It seemed like the other horses wanted to be by the new horse, but Sammy just wouldn't let them. Sammy wouldn't let the new horse eat, drink, or even come close to them. I put him the other pasture, but he seemed lonely. Should I just buy him a goat, or try to work the problem out with Sammy?