Bettas breathe air...
Good point. I wasn't even thinking about that at the time. Thanks for reminding me. Still, I think freezing is more humane.


I change his water about once every two weeks,
That is WAY too long between water changes, especially for a betta in a bowl. You need to change his water AT LEAST twice a week, I'd say.

If you get another betta, please consider getting a five gallon tank with a filter and heater. Although bettas are tough fish, and can be forced to survive in a small amount of dirty water ... it is certainly not a natural or good habitat for them.