Oh, here is some hope for you, a little story about a clown loach that had three diseases at one time:
My biggest clown loach was at the surface of the tank one day, and I noticed that she had not one, not two, but three diseases. The diseases she had were: ich, fungus infection, and swim bladder disorder. She fought those three diseases with all her might. I fought right alongside her, I was not going to lose her without a fight. I treated the diseases one at a time. Treated the fungus infection first, because she never had it before, then after the treatment I did a water change and treated the ich, which took two rounds to get rid of. After treating the ich, I had to sit back and keep an eye on her as she was still at the surface of the tank. I saw her float in the water, not even moving, but still alive. It then dawned on me that she had swim bladder disorder. I quickly gave her peas, green beens, and any veggie that I had that she could have. I also did water changes, which seemed to help her, but she was back at the surface. After giving her veggies for a few days, she started feeling better, slowly. I continued to give her veggies until she was back to normal. It took three weeks for her to get better. While she was fighting the diseases, she saw that I was clearly very distraught about her being sick, she proceeded to hold a plastic leaf with her front fin, and also bite the stem of a plastic plant, which made me laugh. She did get better, she fought off the three diseases. I named her Baby Girl, she was 7 inches, and 8 years old.
So if a clown loach can fight off three diseases with the help of its owner, then your betta can fight off the diseases that it has with your help.
Fish are not just pets, fish are family and should be treated like family.