Here's why:
* Homographs are words that are spelled the same but have different meanings.
* Homophones are words that sound the same but are spelled differently.
In this case, "YOUR" and "YOU'RE" are homophones. "YOUR" is a possessive pronoun, while "YOU'RE" is a contraction of "you are".
The sentence is using "YOUR", which refers to the person being spoken to.