In my last comment I forgot to leave my interpretation for "leave me no room for doubt."
In accordance to what I said before, She keeps repeating "Please sleep softly, leave me no room for doubt." I think she is pleading that he is sleeping and is not awake when she leaves him for good, and leave her zero margin to believe that he is in fact awake and just letting her leave him.
In my last comment I forgot to leave my interpretation for "leave me no room for doubt." In accordance to what I said before, She keeps repeating "Please sleep softly, leave me no room for doubt." I think she is pleading that he is sleeping and is not awake when she leaves him for good, and leave her zero margin to believe that he is in fact awake and just letting her leave him.