As you know, horses don't do well alone. I think you're right. It seems the main problem with your guy is probably excess energy. Young male horses play a lot and if his playmate is now gone, you are it. Fillys usually aren't as rough and tumble as geldings, but just having another horse to run around with will help The sooner you can get her the better.
If you don't do much ground work with him, I would start check out Alexandra Kurland's clicker training books or videos at www.theclickercenter.com or try some Parelli, Clinton Anderson or John Lyons (clicker training also works well piggybacked with these other techniques) type ground work and establish a good partnership AND leadership role with him. If he nips you make a loud squealing sound and flap your arms around a bit, don't hit him. They learn pretty quick that we can't be nipped like a horse. If he always nips in similar circumstances, avoid those for now and until you have a little more control. Interact with him with a halter and lead. Get him a toy, a jolly ball, a Buddy Bopper http://www.horsebuddybopper.com/ , Snack-A-Ball http://www.shanestack.com/shop/index.php?page=shop-flypage-6534&ps_session=d667314e3b80b51c77a0d44bac3c8e07 or something similar. Cherie
