Celie is glad when Shug comes around, because Albert obviously loves her, and seems to mistreat her less whenever Shug is around. Shug regards Celie as a somewhat curious creature at first, not really knowing the full story of Albert's cruelty and their forced arrangement.
But as the story progresses, the two women become friends, and Shug takes it upon herself to show Celie that she does have inner beauty and self-worth. Celie begins to stand up for herself, with Shug's help. This gift causes Celie to fall in love with Shug, and the bond between the two women quickly grows stronger than that between either of them and Albert. This eventually leads to Shug liberating Celie from Albert's grip, in effect, saving both women in a personal sense.