P.H.
it is a phase and can come and go. He needs some time away from you as in a day out with Daddy and then he can see he can trust Daddy too and know you will be there when they get back.
There is not too much you can do being a stay at home mom, they are with you all the time but sometime with other family members or a babysitter coud help his issues..he is worried when he cannot see you. My son is 5 and still 'misses' me all the time.