You're so welcome! I'm still pretty new to the hobby myself, but you sound a bit like me - very invested in wanting to make it better, feeling guilty that it happened, and confused by conflicting advice from different places. It's a tough hobby to get into at first, because the learning curve is so steep, and when things go wrong, it can be hard to get them on track again.
I notice you said that others were telling you to stop the salt, so I knew you were getting conflicting advice from somewhere. In my limited experience, while I haven't seen it happen here so far, on other places like reddit, have seen beginners get torn apart for making mistakes and "not doing their research" (even if they were following advice from a pet store employee. Logically, most people would think that a fish store employee would have the best advice, but it's frequently very bad, especially from the big box stores). People try their best and follow bad advice, then lose their fish and leave the hobby.
If you go to any website where people sell second hand fishtanks, you'll see plenty of adverts for "complete starter kit aquarium, only been used for three months." Look at the photos and you'll often see a tiny tank or fishbowl, no filter or heater, and some betta or goldfish food. They didn't do their research, or were given bad advice and didn't cycle their tank properly, fish died, tank gets sold and they leave the hobby. Makes me very sad.
I would rather encourage people to stay in the hobby, especially people who are passionate and dedicated. Again, haven't seen this happen here yet, but I spent some time on reddit, and while there were a lot of very knowledgeable and helpful people there, and it's a great place to see some stunning tanks - there are also people who love to tear apart a beginner or someone who has been misinformed. Almost as dangerous are the people who think they know what they're talking about, and act as if they're experts, but are just repeating something they read somewhere without checking the source, and give out misinformation and myths. I still find that overwhelming at times.
I get upset when things go wrong with my tanks, and need some encouragement, so I know how good it feels to get that reassurance. I had a sub adult guppy that had most of her tail torn off right down to the body when she got caught up in the sponge filter I was removing to clean, and she fell to the floor. I felt so bad. Had to do salt treatment, and she had fungus the next day. But she recovered, her tail grew back (just a minor scar) and she's now a large, very robust and healthy mother guppy. And I truly mean it when I say that you're doing everything you can for him, so don't beat yourself up, it looks as though you inherited this problem, and you're being proactive in fixing it. He has a very good chance of recovery.