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This was a short story I read in the early 2000's. The main character is a woman and it starts off talking about her life and her husband/boyfriend who ends up passing away. She ends up taking a new pill that stops people's aging completely. The entire world no longer ages and as centuries go by, they no longer need their physical bodies and can choose to leave their bodies behind and explore the universe as a type of energy. The woman chooses that path and the story is really about the experience of living "forever" and transcending into a purely mental/energy state.
If anyone has any leads I would very much appreciate it. I read this story over ten years ago and have never forgotten it.