According to Cramer et al., women are slightly more jealous overall than men (r = .29). However, women experience a type of jealousy which is more closely described as romantic jealousy. They are most distressed when they imagine their partner involved romantically or emotionally with another female. 

Women have a short mating period. As they age, they become less valuable to males, and it becomes more difficult to find a mate. As well, it becomes more difficult to reproduce. Because of this, maintaining relationships and procuring a mate is significantly more important to females than it is to males. Females stand to lose stability and resources when they lose their mates (Buss, 2000).  Males traditionally held a role in which they were providers, while women maintained the household.  For a female to lose their male to another female, she would stand to lose any stability which she had for herself and her offspring.  This could have dire consequences.  While losing a mate to someone sexually may be temporary, losing them emotionally may be permanent, causing a significant decrease in resources.  This is thought to be how female emotional jealousy has evolved (Buss, 2000).

picture taken from  https://fruitfly.files.wordpress.com/2007/07/jealous.jpg on March 15th 2009