My parents have had fish since they moved in together and Bettas about as long. We've found that they live longest in smaller tanks with space where the filter wouldn't disrupt the water. I've had about 5 in the past 3-4 years, Captain Jack, one I can't remember, Eli, Simon and Captain America. Jack was in a 2 foot tank (not sure how many gallons that is) and the poor thing got really ill but would not let go
Eli lived for ages and went peacefully, Simon disappeared into oblivion and Captain America is with us now.
I get more attached to the Bettas than to the others