Technically you can live forever in a universe that is completely empty, it'll just be a lot of cold dark nothing for eternity.

Living forever is such a strange desire, considering that complex life has existed on earth for just a fraction of the time it has existed, and humanity even less than that. I recommend watching the Kurtzgesagt video called All of History in one hour (https://www.youtube.com/watch?v=S7TUe5w6RHo&t=3670s). It displays all of earths history in one hour, and humanity is merely a few seconds of it.

Earth is ~4.5 billion years old, that's 4500000000 years, and in 1300000000 years it will be uninhabitable by humans, and in another 4.5 billion years (roughly 3.2 billion years after becoming uninhabitable) it will be engulfed by the sun.

Assuming humanity manages interstellar space flight you could possibly escape earth and live somewhere else until that also dies, but in case it is not practical or possible, you get to enjoy 3.2 billion years of literally choking and being burned alive on earth.

Assuming you did escape earth (or you're immortal so escaping doesn't matter) In 1000000000000 years the last star will be born, and in 100000000000000 years the last star will die out.

You now have an extremely long time to enjoy suffocating in hard vacuum with your body being boiled by the low pressure, and all in complete darkness until the heat death of the universe occurs in roughly 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 years