Generally speaking, the life expectancy for a betta is about 21/2 years so you must be doing something right. I don't know the depth of the container or bowl you have him in but if you could possibly reduce the water and give him a more confined area it could possibly help. I know such a confined area seems cruel but bettas are found in the wild in small confined areas such as foot prints and under rocks and when given a larger area they try to confine themselves. Another way to reduce stress is to keep them away from light and darken their environment.