My lo was finally use to being gone for a few hours from me when I was taking summer classes. Now…

My lo was finally use to being gone for a few hours from me when I was taking summer classes. Now I've had a month break and start up this weekend. He cries Everytime i leave the room and isn't content till I'm holding him. Not only is it exhausting but I'm worried about leaving him to start nursing school. Any advice?