Frequently, people interchange the words jealousy and envy without appreciating the difference between them — if anyone cares.  So how do they differ?  Dictionary definitions do not often help.  For example, Google dictionary offers the following definitions: 

Jealousy:  “The state of being jealous.”  Well, how much did you learn from that definition?  Now, we must define jealous:  “feeling or showing envy of someone or their achievements and advantages.  ‘He grew jealous of her success’.”  That definition may shed a little more light, but unfortunately uses the very term, “envy,” that we seek to distinguish as a substitute for jealousy.  Therefore, this definition fails to support a difference between the two.

 Fortunately, the definition of envy carries an unambiguous straight forward definition.  For example, as a noun: “a feeling of discontented or resentful longing by someone else’s possession, qualities or luck.”   As a verb: “desire to have a quality, possession, or other desirable attribute belonging to (someone else.)”  Goggle dictionary.com.  Now that we are clear about what envy involves, how does jealousy differ?  Lets look at another source:

— “Envy is when you want what someone else has, but jealousy is when you are worried that someone’s trying to take what you have.”  www.vocabulary.com.  Aha! — Like a breath of fresh air, more clarity enters the room.  The words jealously and envy are not interchangeable.  Even Psychologists agree.  

— “Envy occurs when we lack a desired attribute enjoyed by another.  Jealously occurs when something we already possess (usually a special relationship) is threatened by a third person.”  (What is the Difference Between Envy and Jealously? by Richard Smith, Psychology Today, January 3, 2014.)

Accordingly, of the two terms, jealous or jealously become the misunderstood terms, and usually involve a love triangle, comprising at least three people:  The lover, who has got a good thing going, the lovee, who may have a roving eye, and the interloper, who envies the lover’s relationship with the lovee.  Obviously, the interloper experiences envy for the lovee relationship and seeks that relationship, while the lover is jealous of the interloper’s quest for the lovee.  Got it?

Perhaps too simplistic, but envy usually involve two persons or things, but jealousy almost always require at least three.  

To be sure, jealousy aside, I envy writers that can make a complex subject easy.