What are your gH, kH, pH, ammonia, nitrite, nitrate and any other parameters you have information on? What is your betta housed in, a bowl or a tank, filtered or unfiltered?
Please do NOT attempt to lower the pH of your water with chemicals. The chemicals in products such as pH down generally consist of acid which can be dangerous to play with and will not stablize your water at a lower pH anyway. You can instead end up with pH fluctuations which are much more dangerous.
Your water may be to blame for your bettas behavior but it is not necessarily the gH or pH themselves. Most fish can adjust to a relatively high pH or gH. The things in your water CAUSING the higher pH and gH could be the issue.
If you have well water it could contain harmful contaminants. Even if you are just using the water for yourselves you may want to have a full test done by a lab to see what kind of metals and other contaminants are present.
If you do think your well water is the issue then it may be better for you to use RO/DI or distilled water and adjust the parameters yourself.
Note: you can NOT use straight RO or distilled water since there is no buffering capacity to stablize your pH. You will have to use a product such as RO RIGHT which contains necessary buffering and minerals, or experiment with baking soda to add buffering to your water. (I would recommend simply using RO RIGHT since it would be the most convenient and safest).
You can also try mixing distilled water with your well water for a short term solution. If nothing else it will at least lower the level of contaminants. Again, do NOT use straight distilled water, there is no buffering to stablize your pH.
Here is a simply explanation of kH, gH and pH
but there is much more to know than what is written there.
Of course, your water may not even be his issue. Maybe he's just bored. It's not really uncommon for a betta just to sit there when he's bored. He could be old or sick.
My first betta just died not that long ago at 2 yrs old, so they don't necessarily live that long. He was extremely healthy, lived in a filtered tank and had no issues whatsoever that we could see, he just died one day. Storebought bettas aren't really bred for health and longevity so don't feel too bad if yours doesn't have an extremely long life span.