Ponies and horses.

I have owned and loaned ponies since 2001.
First loan was Boo Boo. He stayed 1 month and nearly killed me and OH by his behaviour on separating from his field mate.
Second loan was Jess. She was a gentle giant and may have stayed a bit longer only the field I kept her in was trashed with over-grazing. She was sold to the riding school where I had lessons. She was too big for me anyway, although she was sweet.
I borrowed one of their ponies but she bolted with me on the first day so she went back to them,
Then I bought Tanzy and after she backed into walls at alarming speed, galloped around the school and wasn't safe to hack out in company or alone, she went back before the end of the one month trial.
I then got Sophie, pictured. I had Sophie for 18 months. This picture was taken from her new home with her teenage owner. Sophie wasn't as fat then! She lived at a farm and small riding place and the owners, with whom I became friendly, helped me a lot to get her going out alone. She was ridden by others and the arrangement worked well. I had an idyllic summer with Sophie but then we moved to sandalfarm. I had Storm, a retired pony from the same school that took Jess. After only 6 weeks Storm died and Sophie went back to the farm with my friends.
Lacking the facilities (no stables at that time) or a companion for Sophie, I sold her reluctantly.
I rode other people's horses for a while, Brandy being the most long term of these, then bought Paddy without too much consideration and sold him just as quickly. He just didn't like me, nor me him. He wasn't cuddly at all. 2 months after I sold him he died of a heart attack at 12 years old.
I went back to riding schools then found a nice local place for livery, a woman wanted to have company for her own horse.
I bought Thor, a Norwegian Fjord. I had him for a year. It was a miserable year and I only rode him with fear and trepidation. He had a massive "nap" and just set off for home without any pre-warning.
I kept on riding at a local school which was fun and stress free. Then I hurt my back and 18 months later have not done much with horses at all.
The yearning doesn't go away but I promised I would never never buy a horse again and stick to dogs, cows, sheep etc. But my friend is down-sizing and she mentioned putting one of her school horses out on loan.
What should I do?