Separation problems

Well my son is 6 and half and is having a hard time being away from me. I'm not due to have my second baby til may 28th. But he won't stay the night at either one of his grandparents unless I stay and he has hard time going to his dad's. When he's at his dad's he has to call me and talk to me all day and night. If we're hanging out with family or friends he's always hovering all over me. Idk what to do help with his separation problems.