My sincere sympathy
I still remeber the first fish I lost. I felt terrible taking, like I just took it home and killed it.
Remember though, this hobby is all about patience. I have had a few times where I felt like tossing in the towel and putting an iguna in my tank. Bear with it, you will see as time goes on things make more sense, and you will not loose fish. Even the greatest aquarist will suffer loss from time to time. At least you care, and tried to help.
I would spring for a small QT
tank. You can get a full setup for like 50.00 and it may save your fish next time.