I was just wondering if there was anyone in the rainham area who wants to share or has a horse I could loan?

You simply cannot share a horse.
Horses are big, but sensitive animals that require lots of responsibility! Owning a horse can be a big step, and you must know how to take care of it. Do you have grooming supplies? What about a saddle? A bridle?

You can lease a horse, which means that you basically rent the horse and then you can buy it sometimes or keep leasing it.

Also, nobody knows what rainham is. Please be specific and add more details.