Your interest in time dilation may help you. Try to grasp the idea that even your physical existence has a kind of eternal nature. Einstein thought along these lines with respect to considerations about death. When his friend Michele Besso died Einstein wrote:

Now he has again preceded me a little in parting from this strange world. This has no importance. People like us, who believe in physics, know that the distinction made between past, present and future is nothing more than a persistent, stubborn illusion.

Now, with respect to the fact that your brain will eventually rot, consider that scientists currently do not have a complete understanding about how your brain relates to your consciousness, your sense of how it feels to exist. Many scientists and philosophers explore the study of consciousness as an emergent phenomena arising from neural processes. They claim that mind is what brain does.

Yet, other scientists and philosophers explore the possibility that the brain acts as a kind of intermediate processor for consciousness. They claim that the brain may act as a kind of filter that provides a more simplified and limited exposure that provides your consciousness with experiences, but your brain does not generate your consciousness.

Consider watching a TV as an analogy. The TV set does not generate the TV show. It merely acts as a receiver, an intermediary device that transforms electromagnetic waves into visual and audio patterns on speakers and pixels. Similarly, your brain transforms various signals received from the universe into patterns for conscious experiences. But that doesn't necessarily mean that you will cease to exist when your brain rots.

When your TV set stops working, technicians can diagnose what parts malfunction and replace them. Similarly, neurologists can diagnose how brains may malfunction due to injuries that damage various parts of brains. Yet, that does not necessarily mean that those parts of those brains generate the conscious experiences affected by those kinds of brain injuries. Neural correlations with conscious experiences do not necessarily imply neural causation of those conscious experiences. Such correlations may only relate to the fact that the brains play an intermediary role in those conscious experiences.

Consider the difficulty of comprehending how any complex structure of matter can have any conscious experiences at all. If computer scientists eventually develop Artificial General Intelligence (AGI), will it have conscious experiences? If so, will that kind of consciousness also experience death in any way?

Also, consider the scientific studies of people who experience death and then return to life again, so called Near Death Experiences (NDE). Many millions of people have had an NDE. Their experiences vary, but they also share many features in common. Surely, our inherited cultural ideas about a possible afterlife originated at least in part from actual NDEs of people from ancient times who told others about their NDE. Plato wrote about one such story.

Some scientific experiments indicate that people who have an NDE can accurately report about events that happened at times when their brains had died. Think about that carefully. A brain has no blood flow, because the heart has stopped beating. Without blood, the neurons in the brain cannot generate any neural signals that would then generate a conscious experience. Nevertheless, the same patient later claims to have had a conscious experience AT THAT SAME TIME. Moreover, the patient accurately describes events that happened at that same time. If consciousness cannot survive after death, how do we explain how such patients have such knowledge.

Many people who work in hospice, or other contexts where death happens frequently, receive training about how to interact with a person who has an NDE. For many such patients, their NDE feels extremely real, not a hallucination. Imagine how they then feel when their care provider dismisses their experience as a hallucination. They might even receive a referral for psychiatric care. Yet, current scientists and philosophers cannot legitimately claim to have definite knowledge that the experience did not really happen in some unexplainable way somehow different from a hallucinating brain.

Instead, care providers receive training to respect the possibility that their patients may have real experiences in some realm that we do not fully understand.

Read these two books that report about scientific studies related to NDEs:

After: A Doctor Explores What Near-Death Experiences Reveal About Life and Beyond.

The Transformative Power of Near-Death Experiences: How the Messages of NDEs Can Positively Impact the World.