Accepting death as a necessary evil

Warning: Mentions of pet death and general pet sickness.

My betta fish seems to be on his death bed. We are creeping up on me having him for 2 years, which is the lower end of the average life expectancy for the fish species. 

He hasnt eaten in 4 days and has been lethargic. I have been sensing there is some other issue then a general sickness. Because of this, yesterday I decided to change the water and clean the gravel to see if that would cause a improvement, but unfortunately since then its gotten way worse. 

For the past 24 hours he has been laying on his side heavy breathing, though he will move short distances and sit up for small periods if stimulated. I tested the water perameters today to make sure it was nothing I did and it came back perfect, so I have come to the conclusion this is just his time to go. Ive put in a underdose of a medication known as Bettarevive  to see if itll help as a last resort, but at this point i am not expecting it too. He was sick when I got him, Im very suprised he made it almost two years with me. I worked so hard to get him to live that first week I got him.

In the end if its his time to go Im fine with that, which feels like a odd feeling to have. Considering how much the concept of my own death freaks me out, its odd that im so accepting of an animals own death. Bht death is a necessary evil and to fight it is to fight a losing battle. Who knows, maybe he will bounce back, but still Im not going to be optimistic when the likelihood is this low. In the end I just hope he is comfortable.

To clarify for any fish owners reading this, he does have a 6 gal tank, live plants, a filter and heater. The water is treated and the water change was around 35%.