I would sort of say Gem is a one person horse,, but the one person is really categorized into nice, caring, soft spoken, good energy people. Any one that is loud, mean, or has bad energy he just doesn't like, and you'll know it. If you approach him in a soft manner and don't push his buttons, he's a great guy.
I thought Vega was a one person horse. She liked me and "opened" up to me as soon as she was mine, and also became very lovey dovey with me, but since we've moved them, I see that I am just someone to hold her hand if she gets nervous or if something doesn't work out with her. She's opened up to the new barn owner and her friend that stops by, and she's quite lovey dovey with Tom too.