well, with no signs of illness I'd have to say it was just his time

, you mentioned that you'd had him for a year or so,most pet shop bettas are about a year old when purchased anyway ,so that made him at least over 2 ....
Sorry about your loss, it's always hard to lose a pet,bless your heart , there's a betta out there that needs a home though & you sound like the perfect person to give him one
