That's actually so ironic that you feel that way, because I've sort of been feeling the same way with my girl!
I have a 7 year old QH mare with osteoarthritis. She's my best friend, heart-of-gold mare. I too am doing dressage at a primarily hunter barn (although since other people have seen my girl, a couple have tried to do dressage since then as well :). Anyway, last winter, riding became so stressful and difficult because she was constantly sore and stiff that I gave her off for three months. We hired the man that is still my trainer (since last winter) and brought her back into work slowly and patiently... She's still having trouble accepting contact, especially with the cold weather in my region and being in and out of work due to that, but still.
Lately I've sort of been feeling discouraged. I know that she will get there (I've never competed and I really want to this year), but it's such a fight for it. She is so stiff, often resistant, and evades the bit like crazy, and riding isn't as enjoyable for me anymore and it used to be. Training her is like a job, and I love it and it's super rewarding, but not when my arms feel like they're going to fall off...
Last week went so much better but yesterday I tried again and it was a horrid ride. I dismounted in absolute tears and practically had an emotional breakdown when I got home (yes, I'm aware that won't do anything for me but it surfaced some feelings that needed to be examined).
So obviously this isn't about me, although I'm probably going to post a thread soon about my issues because it's been really stressful for me, but what I can tell you is that there are going to be people who look at everything rationally and try to use logic and their own experiences to encourage or discourage you and what can I say but don't listen to 'em. It's going to be a fight, especially because your horse has some challenges and idiosyncrasies, just like mine does, but he's your best friend, just like my girl is for me, and I wouldn't trade her for any other horse. She has come such a long way, and if you just keep persevering and keep fighting, I promise it will come. And then you can watch all of the other people's jaws drop when they realize how great you're becoming, and then they can sulk in their own discouragement.