Bettas need heaters. I would suggest you find a bigger home for him (half a gallon is rather small). He should have 3-5 gallons all to himself, with a light and a heater. The water needs to stay 76-80 degrees.
Good day, ladies and gentlemen. I am in the mood to read a good book. I really enjoy science fiction, suspense/mystery/thriller and horror books. Does anyone have any recommendations for me?