Oh I totally sympathise. Same boat, I go back to work next week and my heart it going to break leaving my little boy. He will be in nursery and I am so sad to leave him after spending everyday with him for over a year now.
All I can say is that it will be easier and you will settle into a routine. I've done it once before when my 7 year old was a baby and before long it's all you'll know. I'm finding it harder this time round though and really am not ready to leave him but I have no choice, we need the money (even though half will be going on childcare!).
Stay strong. It will be hard at first but then you will treasure the days off you have together x