why it is difficult for shug?

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.