Mamas boy

My son (he'll be a month old Sunday) is a big time mama's boy. When he wants his mommy he cries and cries until i pick him up and hold him. I dont mind holding him but I'm worried about how he will react when i go back to work. My fiance is very good with him for the most part but when our son wants me nothing but me will make him stop crying. My questions are how long does this need mama stage last? Is there anything my fiance can do to comfort him while I work?