Betta Fish: Sad update on blueberry

Hi guys, I posted in here a couple of days ago asking for advice for my rescued Betta fish Blueberry. He declined extremely overnight, I came home yesterday and he was pineconing – I set up a hospital tank, administered some Interpet Anti Internal Bacteria medication (in UK so unable to get antibiotics) but he’s not getting any better. He’s started gasping for air at the bottom of the hospital tank today and pineconing is getting worse. Is euthanasia the kindest thing to do right now? I don’t want him suffering 🙁