Welcome. Sorry about the circumstances of your welcome though!
Where abouts are you from, on the chance that someone here knows of any good horse vets or farriers(nail men) in your area? Did the vet give you any pain or anti-inflammation medication for him?
Looking at those photos & hearing the story, there's not enough information to be sure, but unfortunately it does seem your horse has suffered chronic(long term) laminitis with mechanical changes - the pedal bone(P3) has 'rotated' in relation to the hoof capsule & has 'dropped' so it is very low in the hoof - that flat sole would be very thin. It looks as though the left front is worse than the right?
I have drawn on a couple of your pictures to get/give a better idea. The green lines show *approximately* how the hoof should be - straight line from hairline(top of nail) to bottom. The angle the top of the nail is growing is most likely to be close to where it needs to be and parallel (in line with) P3. The curved red line is where it looks like the hoof wall is actually growing. The blue line on the sole(underneath) picture shows approximately where I would trim the walls back to, on an angle from the ground. I am not sure how accurate my idea of them is(?) without better pictures & different angles though & if you would like to look at the link below this post and send some more hoof pictures, we may be able to help advise you better.
It looks like it has been a long term problem - at least a lot of months if not much more. That the horse wasn't obviously suffering until after the last farrier(nail cutter) came doesn't necessarily mean it was his fault at all. Horses can put up with a lot of discomfort without being obvious and perhaps it was coincidence that it became too much for him then, or perhaps something happened to cause a strong 'attack' of the 'disease' then. Perhaps the farrier didn't do anything wrong but just the trimming was enough to be too much. But if the farrier cut into the sole(bottom of the foot) at all - it is already too thin to protect inside foot - then he may have caused further problems.
Likewise, depending on what the 'cow food' is, it or the rest of his diet may not be an issue, but as with ourselves, we can usually eat bad food for many years before we develop serious health problems from it, so just because he's apparently been alright until recently doesn't mean the food is alright. If the food has grain in it I would not feed, if it has added ingredients like medecine or vitamins for cows I would not feed. If it is just chopped hay(dry grass) or such it may be perfectly good. We need to know what it is.
I know you already appreciate this, but it's a very serious condition your horse is in and if at all possible, urgent and well qualified help should be found. I would also advise x-rays of his feet if possible. That said, assuming that's just not available, it may be possible for you to heal this horse, depending on how much damage the horse has already sustained from the 'disease' and what you're able to do. It is not something I think it's a good idea for horse owners to attempt to treat themselves without experts present, let alone purely by internet advice, but if you have no other option...
In the meantime, the advice of soft footing is good. You may find that using adhesive tape to stick polystyrene or something like that to his feet will give him enough comfort and padding to stand up and walk around. He needs his nails trimmed as soon as possible, because the walls(outer 'nails') being long will cause more damage and pain when walked on. So long as it is only the outside wall that's trimmed, to sole level and with the long toe shortened, without any tools even touching the sole, this will help and won't hurt him. After his big trim, it is best if he can be trimmed just a little but often - every week or 2 - until his feet are healthier, so that they are kept very short and mechanical problems - walls too long - don't make him worse.
Of course, learning as much as you can is also important, especially as it seems it will be mostly up to yourself to try to get the horse well and you want to learn enough so you have some idea of whether the advice you get is safe
Some more internet sources for information/help... Pete Ramey hoof care laminitis founder horse navicular disease thrush equine foot development farrier Equine Cushing's and Insulin Resistance Information Katy Watts | Safergrass.org
Oh and something you may be trying not to think about...
while I definitely believe there is hope, depending on how much damage to the bone in the hoof, the horse may not ever recover enough to be out of pain. It is also very possible that the horse will never recover enough to be useful. It is also important to consider how much pain the horse is in and how long it might take to get the horse better, assuming you can. In my personal opinion I don't think it is reasonable to allow a horse to continue suffering too much or for too long, so you will need to consider that ethical question too.