Formal:
* Je ne suis rien sans toi. (This is the most literal translation and is quite strong.)
* Je suis vide sans toi. (This translates to "I am empty without you" and emphasizes a feeling of lack.)
Informal:
* Je suis perdu(e) sans toi. (This translates to "I am lost without you" and implies a sense of dependence.)
* Tu es tout pour moi. (This means "You are everything to me" and expresses a strong sense of love and dependence.)
* Je n'existe pas sans toi. (This translates to "I don't exist without you" and is a very strong statement.)
The best translation for you will depend on the context and the specific emotion you want to convey.