was more curious to know what others have been through.
When I first moved here my df and I had only been together "in the flesh" about five weeks cumulatively over a period of about a year. We went through some situations similar to yours....
The constant time together (though he was working, I was there when he left and there when he came home) was very, very tough on him - I depended on him far too much and was far too clingy - making my own friends, gaining some of my old independence and just generally giving myself errands/routines to perform helped enormously. Irronically I have always been VERY big on alone time, but in another country with no friends, I lost that part of me temporarily. He has also always been big on time apart and when we met it was one of the things that attracted me to him. I've always felt, like Carla, that being a whole person and not being dependent on a relationship to make you that whole person is critically important, but like I said, finding myself alone in a foreign culture, I lost that attitude for a while. And I took it VERY personally when he would go straight down the pub after work occaisionally or spend his entire Sunday out with his mates. But what I realized was that in the reverse situation, if he had moved to San Francisco, I would do the exact same thing - I would still need time with my girlfriends on our own and I wouldn't be able to cope with being solely responsible for his happinness - that's too much pressure on anyone. And so now that I'm more settled, have friends, have a routine, am comfortable with the culture, etc. it doesn't even make me bat an eye when he's out after work - in fact I generally turn on some cheesy programme that he hates, pour a big glass of wine, and enjoy my own company.
Another thing that pertains to your story is the bit about changing people. While I think Peedal is right about a relationship taking compromise, I don't think that necissarily involves changing who you are. Jamie made it quite clear from the get go that he is who he is and that he's not going to change that. Luckily I love who he is and don't want him to change (I think compromise is something different) - I've had bf's in the past who I've tried to change, and in my experience it doesn't work.
I realize that this is getting really long, so I'll wind it up by commenting on the anxiety bit. One of my best friends in the US has huge problems with anxiety and it really can be debilitating. It could actually be one of the reasons he's a "loner" (loner or just fiercely independent? I think there's a huge difference) as some people with clinical anxiety (caused by chemical depletion/overproduction in the brain) find it easier to cope by shutting down to others because sometimes social situations that you're not in control of can be extremely stressful. If he would be willing to address that, either by seeing a dr. or a psychiatrist, it might really help both of you. Though I know how the Brits are about that sort of thing ("psychologist? That's what your mates are for" is usually what I get when I tell people I'm studying to be a psychologist....)
Anyway, no advice other than take care of yourself and be careful - I just thought I'd post my experience in case it seemed relevant.