Betta Fish: How do I know when it’s time… Or when he is in pain?

My gorgeous Ziggy (of Stardust) has had this tumor since a few weeks after I got him… it has grown and grown and some of it literally just flaked off. he still gets around fine as far as I can tell (he swims veraciously all over his 9.5 gallon, heated and filtered tank)… but the flaking off the tumor gave me pause. what do I do?😓