K.W.
My daughter and I recently went through this. She goes to a private baby-sitter, so it might be a little different for you, but hopefully this will help. I started to let my daughter "walk" me out. She and I would hold hands and she would walk with me to the door. Then I bend down and tell her that I love her and she gives me a kiss and a hug. Once I am over the threshold we blow kisses and she closes the door. It helped her feel like she was leaving me, not the other way around. With my daughter it was all insecurity. I am a divorsed mom, and she is a little insecure about her surroundings. Make your son feel as "in control" as you can...without him being in control of course. :) I hope that this helps a little, and if you ever need to talk, just send me a message. I completly know what it feels like to do it on your own, and its not fun. :(