I rode this conemerra pony for a while back when I was still taking constant lessons. I loved him to death, but I've never gotten along well with pony's. He and I were doing great for a time, and then he started to take advantage of my weaknesses. In a bad way. I started to get really frustrated and disheartened, and I felt like I was a terrible rider.
I talked to my instructor at the time, and we had me riding different horses for a while. We were able to focus on my weak areas on horses that were better matched. I later went back to the conemera pony, and while he was still a challenge to ride, we had MUCH better rides. I had built up my weak areas enough that I could start to take control back.
The conemera was great for me because he pushed me. We didn't click, and we often times butted heads, but he taught me a LOT. We have different horses in our lives to learn different things. In my case, he was pushing me to a level I wasn't ready for and wasn't going to be able to learn on him. He needed me to be better, and I just wasn't there yet.
I'd definitely talk to your trainer and see if you can't work with some other horses for a short time. Taking a break from the connemera helped lift my spirits as I found that I really wasn't a bad rider, I was just in a rut. The change in mindset was equally as helpful when I went back to riding him as what I'd learned during that time. The worse off you will feel each time you have a ride that doesn't go well will just make you more frustrated. The more frustrated you feel will just transfer to the horse and make it worse.
I'd venture to say you're probably a great rider, but that you may not be ready for this horse just yet. I may have something to do with the more advanced level, and it may not. The connemera pony was a beginner/intermediate horse whose skills matched mine well, so it wasn't that he was too advanced for me. I just wasn't ready to learn those lessons from him yet.