I've given this advice before to others, so here's my little spiel again.
There's three pieces to any riding instruction - horse, rider, trainer. All three are variables, and all can be modified or changed in various ways (with the least amount of variability being 'rider' - you can't be someone else!). So what we have in your case is a year-long horse-rider-trainer unit, that isn't very happy or effective. Rider is miserable and not making much progress, horse is miserable, trainer seems kinda oblivious. You are correctly trying to figure out which variable to adjust.
For a beginner, the 'rider' aspect is pretty much a constant. You can't be a different person and you're already doing everything you know how to do! There's not much flexibility here, and I would say you've spent far too much time already trying to make 'rider' work for horse/trainer -- you, this rider, right now, can't make this horse/trainer unit work.
Next we have horse. By your own report, he's actually a pretty solid guy, but he's been getting pokier and scarier. The relationship seems sour, and he just doesn't seem to *like* you. You, in return, are getting scared and unhappy with him! You know you're supposed to just be confident and The Boss, but amazingly, repeating that to yourself 100x isn't changing how you actually feel. Nor is repeatedly forcing yourself into situations that you don't truly feel you know how to handle, in hopes that you'll muddle through enough to achieve "confidence", doing anything for you.
Which leads me to...trainer. Now here is an interesting thing, because I can tell by *reading your internet post* that you lack confidence, are probably way more afraid now than you ever were in the beginning, and your horse is getting pushy and frustrated. And this trainer has either missed this for 12 months, or has absolutely no idea how to manage it beyond trying to do the same things that haven't worked yet over and over and praying something changes.
My opinion - and I base this on having almost literally the EXACT same experience as you (new, 40's, beginner-ISH horse)! - is the horse is fine, and YOU are fine, but you need different instruction -- that can help you regain your confidence, and goes slower. That doesn't make this trainer "bad", she's just not the trainer the you/horse unit needs right now!
When I switched from "Just Be Confident" trainer to "I will teach you to how to deal with the bratty pushy nonsense, and while you are learning, I will enforce this horse listening to you, and you will start to understand how the levers work, and THAT will make you confident" trainer -- I went farther and felt better in one 45 min lesson than I had in four months.
With the right instruction, after about 5 months, my relationship with my horse went from begrudging tolerance of each other to happy whuffs when I walk up to his stall, friendly nibbles when brushing, and near miraculous willingness to try in the arena. He still pushes - he always will, he's just that kind - but I can deal with it now, and I know he won't do anything malicious. Pushes are now exceptions, rides are not fights. And the pushes are half-hearted, easily corrected, quickly forgotten. What felt impossible 6 months ago is pure love today.
Given how *generally* solid you describe your horse, my opinion is try finding more suitable instruction first. You certainly don't have to give any new trainer a year! -- at this point, I'd give it a few lessons and it either clicks or doesn't. It would also, I think, be very valuable to get an assessment of the horse/you unit from a variety of experienced people (even if you don't pursue further lessons). If you go through a few trainers and you're in the same place, then you've done everything possible and yep, it's time to see about changing that "horse" variable. (Or perhaps a different trainer will assess that this really is way too much horse, and you need a better fit, right off the bat!)
My trainer's background is with PATH (therapeutic riding) and she's patient, creative, and - obviously - all but obsessed with safety. I can't speak for all instructors but PATH is a great place to start looking if you have no other recommendations or ideas. (You can't ride at a PATH stable, but some instructors are willing to travel to give lessons to supplement income).
Good luck! I know this got long but I did want to echo everyone else -- kudos to you for recognizing that the situation isn't right, and it's either too much horse or not the right instruction. I hope it becomes fun again for you very, very soon.