Shug is larger than life, and she sure does know how to love. Her problem is that she loves and keeps on loving, even when she adds other people to the mix. She has a weakness for people, and she keeps people in her life, no matter what.
Shug is the person who lifts Celie up and gives her the will to leave behind a life of victimhood and become a new woman. But ultimately, Shug can’t (or won’t) commit to a romantic relationship with just one person. She needs to be admired. When a 19-year-old admires her, despite the fact that she’s thirty (or so) years than he is, she can’t help but take off with him. Shug will never stay in one place or with one person, but she’ll keep returning because she never discards the people she loves. Although Shug is the person that gives Celie the gumption to change and to leave Albert, ultimately Shug’s inability to stay with one person means that Celie has to find reasons within herself to maintain independence, and not depend on a fickle lover like Shug.