Betta Fish: Is my betta in pain

Sorry, don’t know where my description went.

My betta fish has the tumor pictured. This week he’s been a little more lethargic than usual, but he doesn’t seem to have any problems reaching the surface or breathing. He has, unfortunately, been hiding a lot and is not as curious as usual. Are these signs that he’s in pain? He didn’t eat today which is a new thing for this week. I’m honestly so worried and stressed for him, he’ll be 4 in December and I truly love him with all my heart.