Good news, too. That piece of pea I fed him yesterday must have done the trick, because his stomach is nearly the size of a normal Bettas
His stomach is still a bit big but it's better. I'm going to continue him on the treatment for another day or two, give him some rest for a few days to a week, and because I suspect he might have gill parasites or MAYBE fungus I'll give him a 10 day course of AQ salt, just in case (1 tsp/gallon + daily 100% water changes). Shouln't harm him...
I took a pic. As you can see he has a big belly but compared to yesterdays pic it is tiny. But... I did find the worlds largest Betta poop in the corner of his tank
It had a slightly green tinge to it which I'll assume was the pea. Should I give him another piece of pea to completely clear him or just let him do the rest?