Think about it this way: if the material world is really all there is, then it does not matter whether you disappear or not. The components that formed your body will somehow continue to exist and only the particular combination that you perceive as yourself will disappear. And this will happen to everyone regardless of their accomplishments, religion, wealth, socioeconomic status, education level, physical or mental well-being etc... Material disappearance is the end that is destined for all of us even if there is an afterlife. Also nothingness is nowhere near the worst case scenario for an afterlife: a malevolent God is. If the afterlife is truly structured like how current religions claim it is, then we are trapped in a terrible existence which can only multiply our pains. The best case scenario is a benevolent God who is filled with unconditional love and who is capable of forgiving those who are ready to apologize. Even if this puts burden the most on us (since then we need to repent for our actions), redemption is nowhere near as bad as being trapped in randomness and never-ending existence (the case of the malevolent God). However, the only people who can answer which scenario is the correct one are already dead and the only thing we can do is hope for the best but prepare for the worst. One should hope that there is a benevolent God but prepare for a malevolent one. Nothingness in the afterlife just means that death is a very long sleep and it is neither as good as a just afterlife nor as bad as a injust afterlife. It is just nothing.
That being said, your thoughts read like you are currently overwhelmed with life and emotions. And I know that loneliness is the most cruel punishment a human-being can receive. However, do not engage in any action that you will regret once the storm passes especially if you are scared of what awaits you in the future. First, try to calm down your thoughts. Try to understand why you are in an existential crisis. Is it because your life has lost all the meaning and there is no way to find a new meaning? Is it because society is not compatible with the meaning that you want to achieve? Is it that your meaning can only be achieved through others? Is it that your meaning is currently out of reach? Or are you simply just confused about life? I am not writing this to argue against your feelings of misery because I know that feelings are never invalid. I am not someone who thinks suicide is inherently bad or people should be prohibited from achieving it either. On the contrary, I believe that only the society should be held accountable for suicides unless the act was carried out to run away from a well deserved punishment. In fact, I plan to end my life after my sister is done with her university entrance exams in 3 years. However, I would advise everyone to establish their stance against existence more firmly. Even if that means you will end up hating existence all together. There are people like that among us too and that stance is just as valid as every other stance against existence and it will help you calm down your feelings (even if some annoyingly optimistic people hate to admit it). At least try to spend your remaining time in mental tranquility by understanding your existence better.
