I'll Tell you about my own first horse, she was a lot like this. I was new to owning horses, didn't have the money for the trainers around here, was desperate to get her to come around....put a full year into her.
She was a litle pinto mare I had named Autumn. She was in a terrible home, well fed, but not much care after that was given to her. I honestly thought I'd be doing her a favor getting her out of there. She did ride, but her manners needed work. So I bought her, more out of heart. My first attempt at riding her nearly got me thrown....she reared. Next attempt, she rode out, went towards the field, then threw me off and also fell over. I started lunging her with a saddle on for short periods. I finally was able to ride her, but she wouldn't go far from home. If I got her too far into the field, she'd stop moving completely....just put her feet down and not budge. A kick, crop, spank on the rear, would just make her buck you off. She had a terrible temper and very stubborn. She wanted to stay in her paddock and the only good thing a human was for was to bring hay, grain, and apples. After a year of working with her, lunging, riding, walking her everywhere, there was little difference in her....she grew more and more convinced that she didn't like work. I was never hard on her, never yelled at her, only spanked her behind when I had to really get her moving, never forced her into a bad situation that made her feel threatened. I rewarded her for good behavior when she had it. Then there would be a day or two when she'd ride out nicely, then I thought we had gotten somewhere.....only for her to suddenly decide to turn on me and run back home out of control, no matter how hard I made her stop. I also practiced the one rein stop, she hated bending her neck like that....but in one scary run, I forced a stop on her using it, and it worked. She was so out of control, we were both going to get hurt if I didn't do something quick....or jump off.
So, in my case, after a year of a broken heart because my very first horse was sooooo bad, I sold her to someone who wanted a pasture mate....because ultimately, that was the life that Autumn wanted. I kissed her goodbye, gave her no ill feelings and set her free to a new home. (that is not what everyone wants to do, or can do, I am in no way urging you to do that....but there is also nothing wrong in knowing you have a bad match you're dealing with too). I have not regretted it since. I now have Ella who is the perfect match for me. I have no more problems. Ella is a different story, but I wanted to tell you this so that you know there are similar stories out there. They can all have a happy ending, whether it's what you are picturing now, or not. Just be truthful with yourself. Is this horse changing? Do you see this horse coming around at all? Do you see a future that you want with this horse happening? If yes, keep going, keep working....if not, you may need to try something else, whether it's save your money and get that trainer....or let this horse live in your pasture, or find it someone else. None of these choices are bad, you just need to find what will work for you the best.
I wish you a ton of luck. I know a horse like this is difficult, it's frustrating, and heart breaking....and no one else knows what you are going through emotionally. You need to make the decision yourself on what you're going to do next. You have lots of options. I hope this encourages you, and lets you know you're not alone.