So, Nebula, also known as "work betta" has become a bit sedentary. He was the Betta I kept from the three I took home from a petstupid that shrugged, looked at the fish, and said, "yup, those are probably gonna die overnight." I got him in december. I tried to attach a picture, but Fishlore has not been letting me do so on mobile. He seems in perfect health, but he does not patrol very much. For the first few months I had him, he was pretty active. Then, in April I noticed that he was flaring a TON. Eventually I released he was flaring and trying to bite at the large orange nerite snail. I kept an eye on him, and removed the snail when he started showing stress stripes and clearly was not about to stop. Since removing the snails he pretty much just chills on random leads around the aquarium, or hovers by the glass giving me the hairy eyeball. He lives in a ten gallon all by himself, barring I think one or two black racer merited. He has a 20 gallon rated sponge filter, and no heater, because we keep my part of the office constantly between 78 and 82 (crazy Floridians if you're wondering). His tank has been running for about two years, though I switched the bettas between work and my house shortly after I got him. I do 50% water changes every other Friday. He doesn't get fed over the weekends.
Betta fish have weird personalities. I had one that wouldn't stop flaring and jumped out the tank and died. Maybe you should put some of these in your tank to relax him
Have you tested the water? Do you have the parameters for ammonia, nitrite, and nitrate? It's unlikely anything is terribly wrong in a tank that size with one betta and frequent water changes, but it never hurts to check. Since the activity level changed when his 'competition' was removed, it could be that he now just thinks his territory is safe and there's no need to do anything other than chill. I've heard of people 'exercising' their bettas by holding a small mirror to the tank a couple of minutes a day, but I've never done this, as I'm worried mine might actually strike the glass and knock himself senseless .
