A horse like this needs to have his feet professionally trimmed every 4-6 weeks. If you are jumping him, he probably needs shoes too.
If you cannot afford to have his feet done every 4-6 weeks then you should not have a horse. It is that important. Really it is.
He is not a bad horse. He is a bit light in bone but not a bad Thoroughbred. The top of his neck is under muscled and the underside of his neck is over muscled. This tells me he is lacking in foundation work.. probably travels to the jump head high and I am going to guess he wears a martingale.
So... he needs more feed (he is thin), he needs his feet done NOW and he needs more foundation work.. such as lots of caveletti and trotting up hills and learning to work from back to front instead of front to back. I would lay off jumping for 6 months and get him squared away on flat work, weight gain, building proper muscling and NONE of that until you address a regular farrier schedule.