Betta Fish: URGENT HELP – why is my betta fish so sickly and frail????

I’m extremely distraught over how bad my poor boy grimes is getting. He’s such a beautiful fish and I am at a loss. I have never seen gills look like that before they literally look like they’re ripping apart?! I feel like a horrible fish owner and I am REALLY hoping someone knows what the hell is going on. He’s such a pretty fish and it’s breaking my heart to see him like this… can he be saved? He’s only about a year old and he was the first fish I ever got getting into this hobby 🙁

The tank is a stable 10 gal (nitrate nitrite ammonia 0ppm and I check weekly with the API tester kit). He still eats well but he barely moves anymore and he looks so so so bad it’s shocking to me. The pictures truly don’t show how bad he looks. I just feel like bawling because I don’t want him to die but I also don’t want him to suffer.

The only thing I can think of is that I tried using seachem SAFE with a milligram scale, I read online that it was okay to use in smaller tanks as long as you calculate the dosage right but perhaps I did something wrong and that’s the reason he is like this???

I dosed seachem Safe 40mg because I read that’s the amount for a 10 gal, but I’m thinking maybe I have been overdosing on accident and did the numbers wrong? I stopped using it last week.

Also, I feed him fluval tropical bug bite formula, 8 pellets a day in total. Am I underfeeding him??

I thought it might also be the driftwood so I took it out two weeks ago but still nothing has been improving :((((