I'm sorry about your ribs, hope you feel better soon.
I just wanted to say I feel for you, but I think your horse is lucky to have you. You must realize that there are horses out there that people get on, take for long rides, and have minimal issues, especially with a horse as young as yours. Those horses are why some people say "keep it simple, stupid," and think some people are doing things all wrong or being fussy, and that's why they have problems.
There just seem to be some horses that don't have one minor problem like being difficult to worm, but instead have many issues, even rare ones that all show up in one horse. Those horses need extra special owners, like you. I understand you've spent a whole lot of time, money and emotion on this horse.
I was thinking about all the issues you've had with difficulty feeding, some behavioral things, some physical issues, and then Lyme, and a very rare complication of Lyme where the treatment causes laminitis. Any of those alone would be difficult to deal with.
I sympathize very much, since it seemed like my last horse Halla was similar, with issue after issue her whole life. I'm not saying your horse will always have issues, I'm just saying I understand what it feels like to just have one thing after another with a horse, and always wondering what is wrong with them and doing your best to struggle along and get them better. Trust me, it's not you, it's just the way it happens with some horses.
My mare Amore somersaulted on more than one occasion. Thankfully, she was always super tough and not injury prone even though she was accident prone. Other horses seem to be either illness prone, accident prone or even both.
One thing I tried to think of as being positive was that everything that happened with my horses has taught me a lot that I could use in the future with other horses.