Describe symbolism in Petals on the Wind by V.C. Andrews

In Part II, Catherine begins an affair with Dr. Paul. This affair begins shortly after Catherine turns sixteen, suggesting to the reader that it is similar to the incestuous affair with Christopher that she is continuously fighting off. Dr. Paul has grown a mustache, an important symbol to Catherine whose first kiss from someone other than her brother was from Bart Winslow, a man who also sports a mustache.