Firstly a mssive hun, i know it feels like nothing will fall into place and your going to be making things hard for you both but i PROMISE you wont, i don't know why or how but things just seem to fall into place.

Where possible now can you start making SMALL changes to how you put him to bed etc, maybe get DH to start a new routine with him, get DH to have him for a BOYS DAY without you around at all, just little things now so that it wont be such a shock when your gone for a couple of nights?

I know it's not easy and you feel bad but you wont ruin his life, chances are he will be smitten with your new LO and things will all just fall into place.

Deep breaths and positive thoughts... FWIW i went through all the same feelings.