"I don't want to give you this."
Translation:אני לא רוצָה לתת לךָ את זה.
The prefix -ה means 'the'. It doesn't fit here, the same way you won't say in English "...give you the this".
The preposition את doesn't always come with -ה; it comes before a definite (direct) object. In this case זה (this/that) is definite, so את is necessary.