M.C.
it will get better with time. Make sure you are spending extra quality time with him when you are together. When you drop him off, tell him when you'll be back and make sure you're back exactly when you say you will be. Also, when you leave try to stay positive--if he sees you get upset, it will worsen his sadness. Before all of this, though, make sure it isn't a problem with the school. Best of luck--kids are resilient creatures--he'll do great!