For about 4 or 5 years I lived with my fiancé . She has passed away and left me her half of the house we lived in. do have to move out fast to sell it

Hello.  An attorney will have to review your documents, but it sounds like you do not have to  quickly leave the house if you dont want to.  It does depend on how title is held with the grandson and what the terms of the trust are.  Did she leave her half of the house to you as a beneficairy of a trust or are you a surviving joint tenant?   The answer to that question will dictate your next move.