I am no expert in this…but his behavior sounds like it may be previous owner seeking? Could be that he came from a well loved home, but escaped and got lost...and maybe he misses his family. But I think it will definitely get better. Sounds like you are doing everything right. Don't push it with new people, or people that make him uncomfortable. You can't convince him that he is safe...it just takes time.
Good luck, and good job....
Andrea, I think you could be right because it sounds like what Ruby does and I don't think it is because of fear in my situation.
I can't leave the house with Ruby out of her crate downstairs and leave her with my brother or father (both of whom she loves) and have her see me leave. Otherwise, she paces frantically and gets more and more nervous to the point of really potentially causing harm to herself by knocking over chairs, etc. and they end up having to crate her so she doesn't hurt herself. I've even tried crating her downstairs, and having them let her out, but the problem seems to be her seeing me go out the door to the outside.
Now when I leave her with them, I have to leave her upstairs in a room in her crate and then my brother goes and lets her out. Even then once she is out, she will initially check for me and from time to time get up from resting and start looking for me (but not frantically), but eventually will settle down and there are no problems.
The only way things have gotten better is to have my brother and father take care of her more both when I'm around and not around. I've been having my brother feed her and let her out of her crate when she is done or I've been anywhere…even if we both arrive at the house at the same time. I've also been having him walk her on her leash, while I walk with them. That sort of thing. The other thing I've been doing is if I'm in a room, I'll close the door and leave her outside of the room so she can't constantly follow me but knows I'm coming back.
Even though it has been slow, there have been huge improvements from when I first got her, because back then I couldn't even close the shower curtain without her getting frantic. The first week or two I had her, I had to keep the show curtain open so she could see me.
They key also for me was not to force my brother or father on her...she had to accept them on her terms. She was terrified of my brother because he is 6'5" and I think the biggest man she had ever seen. After the first week, she would start to go around him and sniff him, but he never reached to her to try to pat her...just let her do her thing and talked quietly to her. After about a month, eventually she'd come near him and sit next to him and he would rub her sides and talk to her. Now she runs to him and jumps up on him and stretches out to make herself as tall as possible to see him. He is the only one she jumps up to.
I think it will just take time for your boy to warm up to everyone...