Change in eating habits has me worried

I've had my Crowntail, Finnegin, for 8 months. Since the beginning, he always greeted me when I approached his tank, and he'd wait near the surface while I individually fed him his pellets. A couple of weeks ago, he stopped eating or showing any interest in me and remained perched on his highest plant, "guarding" his bubble nest. His bubbles eventually dissipated from filter/current flow and my cleaning. Finnegin then spent the next week hiding in his favorite cave -- I was lucky if I could get him to chase 2 pellets and eat. This weekend, he seemed interested in eating, but wouldn'd come close to the surface. Instead, he waited for pellets to fall, and he'd catch some mid-range to almost eating off the bottom. I don't know what affected his appetite. He swims fast when he comes up every now and then for air. He looks the same...no bloating, spots or velveting. This morning, I found him back on the high plant, with a line of bubbles that he apparently had been working on overnight. Again, he had no greeting for me and didn't want to eat at all. Does anyone have an idea what can be going on with him? He has clean water and water changes; in 10 gal. tank w/filter and his heater is at 82. I don't want him to starve himself to death. I can't think of any "trauma" or "stress" that would've made his behavior change so suddenly. Thanks for any advice you can give.

I have one like this. Citizen Fish, my tri-band butterfly SD, blows a very small nest most days, hangs underneath it guarding it, and on the occasional days he's not guarding his nest he's asleep on his side underneath a moss ball looking like he is dead. If I open the lid he'll come for food, he shows a little interest when I go over, and he eats as much as the other bettas in the divided tank, but is considerably thinner. He's in the end compartment of the divided tank, his neighbour is an orange crowntail who never bothers to flare at anything and they live next to each other peacefully. He used to be next to another betta who was very aggressive, and they spent so much time flaring that they blew their tails to I separated them as it was too stressful.

I think sometimes adult males just have a massive urge to spawn and get fixated upon the behaviour. He's also got quite a tatty tail but doesn't tail bite or have fin rot, it's like all his energy goes into hanging there on guard rather than building himself up or moving much. I've used several different medications over a few months to see if anything helped his tail or weight, but nothing has improved it and he seems healthy other than this odd behaviour. I'm really not sure what else you can do, maybe try exercising him with a mirror to flare at for a few minutes a day, or add a toy for him such as a table tennis ball.

Some of my boys are really lazy. Just come up every now and then for food. Some others bubble nest all the while. As long as his water is clean and warm there isnt much you can do. Mirror time might help.

Have you tried different foods? I vary their diet and haven't encountered that
problem to dater.

I do treat him to shrimp and bloodworms and a piece of a pea once a week.

So doesn't have much interest in anything then. I hope he snaps out of it.