Betta Fish: At what point do you euthanize a fish with tumor?

Hello,

I have a betta, O’Leary who has a tumor, I noticed it in July, it’s been steadily growing and I’m starting to think that it’s going to break the skin (scales)

He’s still eating, swimming, and active, however I have noticed his back fin is ‘twisting’ or like folding in on its self, he is also losing weight. I can’t get a photo as he doesn’t hold still long enough for my camera to focus but I will attach a photo of his fins (the discolored scales on his side is the tumor its hard to see in this photo but it’s very obvious from the top view)

I think he still as a good quality of life for now however I want to make sure I don’t put him though unnecessary suffering once the tumor starts causing pain

Thank you