Yes, I have been over every scenario in my head - costs, future heartache, inability to re-home if necessary but I keep coming back to the fact that I have bonded with him in a big way already and couldnt ever forgive myself for him being sent to the works. I have already been out today and spent about $100 on joint supplements and other minerals so the costs will probably start adding up quite quickly. Given that I only want to ride for pleasure and it will only be 2-3 hacks per week I want to persevere with trying to get him to the point where I can at least ride him safely. If that doesnt work then I have a friend who runs a horse sanctuary and could look at rehoming him as a paddock mate or as a last resort put him down humanely, at least I would know he didnt have to endure the possible horror of ending up at the meat works. So no more riding at this stage, we are starting from the ground again using the information other people provided. Thanks everyone for your input, hopefully there will be a happy ending for this little guy.