How do I handle being the person the whole close depends on?

You know the financial systems better than anyone, and it made you indispensable, which sounds like a win until you feel its weight. When the whole close leans on you, the value is real and so is the trap. Time off is hard. Mistakes feel enormous. You are never quite able to step back. Being the single point everything runs through is good for job security and bad for almost everything else, including you. The knowledge in your head is only powerful when it is yours alone, but that same aloneness is what chains you to the desk. Depended on is not the same as valued, and it is definitely not the same as free. Start giving some of it away. Write down one process only you understand, or teach one colleague one part of the close. It will feel like loosening your grip, and it is. You are not making yourself replaceable. You are making yourself able to rest, and building something that outlasts your own exhaustion.