The Good Mother by Sue Miller

Recently divorced, Anna Dunlap has two passionate attachments: her daughter, four-year-old Molly, and her lover, Leo, the man who makes her feel beautiful -- and sexual -- for the first time. Swept away by happiness and passion, Anna feels she has everything she's ever wanted. Then come the shocking charges that would threaten her new love, her new "family" ... that force her to prove she is a good mother.

Hardcover, 1986

Goodreads: 3.82