Here is a website with some info on care for bettas. It may be helpful.
This is what it says for lifespan.
Lifespan: 2-3 years
If he seems bloated he may be constipated. try not feeding him for a day to clean out his system. If he still seems bloated you might try a salt bath but that is info you'll have to look up on the internet or talk to a vet about because I'v never done it.
You may also want to take the temp of the water and make sure it's not too low. He may need a heater.