This sentence expresses feelings and thoughts that are very important to you. Without you, no matter how short life is, I will feel unhappy and lonely. Your existence is one of the most important things in my life, expressing my endless love and cherish for you.
This is a very romantic and affectionate expression, usually used to express strong feelings and desires for the other half. Whether in love, friendship or other relationships, this sentence can be used to express your importance to someone.