I can't speak for all women, but I can tell you what I have experienced and believe.
There are a handful of people who are disturbed and pathologically jealous, (both men and women) but they are in the minority.
Men and women can be jealous - it's not a trait that belongs to women.
When women are jealous in a romantic relationship, it usually means they're not sure of their footing. Sometimes this is because of bad past experiences, and sometimes they are correctly reading a problem with their partner. (Remember the old expression, "Just because you're paranoid, doesn't mean no one's following you"?)
A twinge of jealousy happens to everyone now and then - it's a sign we're human. If you rarely invest in anyone emotionally, you're pretty safe and may not feel it much.
Falling in love makes everyone feel insecure (fear of losing their loved one). No matter what anyone tells you, there are no exceptions.