@FastFood
I've always found that quite distressing too OP.
I remember a woman I knew, she had a horse, there were photos of the horse on her facebook, in her house, pictures of her kissing the horse's muzzle...and then she sold it for a new one.
I understand that a horse is a living tool, but still, I can't help but feel sad about that.
I sometimes contemplate getting a new bicycle, but the thought of selling my current one breaks my heart.
So selling a horse will definitely be impossible for me.
Surely you can see the difference between a bike and a horse, though? Your bike, after the initial outlay, isn't going to cost you any more, unless it needs a very occasional repair, and most bike repairs are easily doable yourself.
A horse can't just be kept in your shed, and its regular costs are eyewatering if you don't own your own land and don't do all the daily care turnout, mucking out, poo-picking, exercise etc yourself. A horse needs grazing and some form of shelter, hay or other supplemental feed, bedding, shoeing (even if you keep your horse barefoot, it will need a regular trim from the farrier), grooming, tack, saddler, supplements, vet costs, dentistry costs, vaccinations, worming, insurance -- livery in varying grades of expense if you can't keep your horse on your own land and do all care and exercising yourself etc etc. You'll need your own clothing, boots, hat. You may need to pay for lessons, access to an arena, to have your horse professionally schooled, physio, or transport. If your horse is kept at home, you may need a companion animal.
Even if you are the most sentimentally-attached person in the world, and are, for instance, OK in theory with keeping a horse that your child has outgrown, or which (the horse or your own) age or injury means you are now unable to ride, and /or you have lost your job and are suddenly penniless, you may have to recognise that you cannot keep your horse. And that it may not be in the horse's interest to be kept without company/regular exercise etc.