Most on here are not offering advice from a position of superiority using internet acquired knowledge.
Instead you are getting mostly actual personal experience based advice painfully acquired over many years and offered to help others AVOID such experiences and mistakes.
Sometimes such advice can come off as curt but should be taken as direct, not rude. At all. And its just advice offered as things to think about without having all the details, not absolute judgement or the single one and only answer.
Based on my experience, riding twice a week with a Green or “ project” horse generally doesn’t work like it does with a packer who does not forget last weeks lessons without training ride$. Depends on the specific situation.
Speaking of things to think about based on my experiences, trainers operating costs are ever increasing and most cannot afford to carry lesson horses off the beginner level. Probably why it sounds like OPs trainer only has one available so there aren’t many options staying in current barn. No shade on OPs trainer or OP, but thats what it is. If thats working for both, no problem.
But…it may not continue to be a viable option. Things happen and its always a good idea to investigate other options so you don’t have to make a decision when upset over a sudden change.
I had a trainer I liked very much thank me for being there for almost 2 years part leasing/ riding extras but it was time to either buy, full lease or leave and her business couldn’t support clients like me. Have friends who had the same experience and seen barns require lease or ownership in their lesson program. They cant afford to carry extra horses just for pay by the ride lessons.
Have had trainers get kicked out of barns they were leasing stalls in, suddenly move out of the area, get married or divorced and drop public lessons and had one long time trainer die.
Don’t get caught unprepared. Stuff happens, mistake to assume things will go on as is for the forseeable future. Maybe you stay lucky but maybe not.
Like I said, this is just something to think about, not telling you what to do. Just think. BTW, been boarding since 1970 so, yeah, things happen without warning.