I'm sorry, op I do sympathise which you to a point, but am I the only one who looks at this and thinks, so, you were happy to take the horse on for a year but you didn't plan it properly, you could easily have insured it with another company, you want to use it but only seem to want the perks, now it needs a bit of attention you want to chuck it on the rubbish heap. You agreed to have it for 12 months, I'm sorry but although I agree you can probably get out of this, you did make an agreement, it doesn't matter if it was on fb or on paper... It's an agreement. I have to say if I were the owner I'd want my horse back anyway because someone who takes my horse on would be expected to live in the real world and take the rough with the smooth. If the horse hooned around in the field, hurt its leg and was off work for three months, you should still feel obligated to care for it. If I was loaning my horse out and someone was paying towards his care I'd be really ticked off if he was unridable and they wanted to shirk their financial responsibility. You know how much horses cost, what can go wrong, the financial implications, you took this horse on but you are not willing to care for it as if it were your own which essentially it sounds like you initially agreed to do. Sorry but I don't have as much sympathy for you as others seem to do. I do have sympathy that you haven't had a perfectly healthy horse all throughout (but then that's life). I do have sympathy for the owner who assumed her horse was in a safe caring home (not such a great assumption). My greatest sympathy goes to a horse that no one seems to want or give a damn about and who faces an uncertain future.
Somewhere you state that you have never bonded with the horse, you also say you had a trial period... Why did you take the horse on then after this, oh yeah, because it suited you, now it doesn't.
Nope, sorry but not much sympathy for you or the owner. Poor horse