I have a 16.3 that is retired through unsoundness. I am in a position to be able to keep him for the moment and he likes being retired. However, I will have him pts when his lameness gets worse. No one wants a big horse as a companion, they want cheap hardy ponies in my experience. Please dont consider trying to sell him as unscrupulous people are many and he could have a very miserable existence. I think you should have him pts, you say he is such a burden and this will make you resent him eventually I think. I have had a horse put down previously and he really didnt know what was going on, I felt terrible for weeks, but he was out of his pain.