You have two betta in one tank? And the NOT fighting? That's near impossible. Is a male and a female? Hopefully not 2 males. How big is your tank?
He probably got constipated from eating the food for other fish. A few months is a set up is just a trial period for any tank mates. You won't know if they truly get along if it's been a lot longer than that. Sometimes it takes months & months for things to happen.
Dropsy at the pine coning stage is usually fatal, from my experience. Try him on meds and see what happens. Good luck.
