However, I can understand what the writer is trying to convey. It likely means something like:
"I miss you here very much, you are my whole world."
Here's a more grammatically correct version:
"Te extraño mucho aquí, tú eres mi mundo entero."
Here's a breakdown:
* Te extraño mucho aquí: I miss you very much here.
* Tú eres mi mundo entero: You are my whole world.
This version is still a little awkward, but it's a more accurate translation of the intended meaning.