Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I'm so sorry to hear that Riley's tail has a sore on the end of it that he is chewing on, despite your best efforts to stop him. This sounds like happy tail, which is a condition that occurs when a dog wags his tail and traumatizes the tip repeatedly on a hard surface, such as on furniture or walls.
If he is chewing as aggressively as it sounds like then this will be almost impossible to clear up with just home care. It appears that this has turned into a deep tissue infection which is both painful and itchy and topical treatments/ointment only seals in the infection.
I would recommend a big Elizabethan (lampshade) collar so he cannot reach the end.
But I also recommend that he see his veterinarian for oral antibiotics to treat the secondary infection, which may need to be given for several weeks.
I also recommend sedating him, debriding his wound and using a laser to seal the nerve ending and blood vessels at the end of his tail. This helps tremendously with pain, bleeding and the urge to lick and chew his tail. This can allow healing and save the tail tip.
In some cases pain medication and a sedative or anti-anxiety medication need to used for a period of time to break his chewing habit until he heals.
Your veterinarian can show you how to use an empty syringe or syringe casing to make a protective bandage over the tip of the tail that still allows air to circulate. This is not easy to do as incorrectly bandaging the tail can lead to cutting off the blood supply and make things much worse, so have someone show you how to do this the right way the first time.
In severe cases we sometimes need to amputate the tip of the tail if the damage is too severe. If the infection spreads too deeply it can involve bone or even get into the spinal cord canal.
Please let me know