How old is he? It looks like a tumor, possibly caused by genetics or ripping his fins. As long as he’s still eating and swimming it should be fine. Also nix the melafix, it’s harsh on labyrinth organs. Instead treat with warm clean water, api aquarium or epsom salt and katappa leaves, or rooibos tea. He seems to have been fail biting too, unless you have decor or other fish that is ripping him up.I have this Betta and he has had this spot on his top fin for a couple of month's I have treated it with Melafix and BiFuran with no change.. He seem happy .. Will this end up ... You Know.... Killin him and how long can he stay like this?