Here is the definition our friend gave, it's not exactly what the dictionary says, but it is exactly right.
Jealousy is when you are afraid of losing something. You are jealous of the girl flirting with your boyfriend because you are afraid she will steal him.
Envy is when you want something you don't have. You are envious of the girl with the gorgeous boyfriend because she has something you want but don't have.
This has explained a mystery for me.
In the Bible God is described as a jealous God in several places. I have wondered for a long time what that means, because I could not see how that it is a good thing to be jealous, even when applied to God who we know is good, so His jealousy must be good. It just didn't make sense.
But with my new definition it makes perfect sense.
God loves us in the extreme. He is jealous of anything that might take us away from Him. Things that rouse His jealousy make Him angry, because He doesn't want to lose us. Losing us means we die. I guess He has a right to be angry. I'd even go as far as to say the anger of God is a beautiful thing.
Of course with people jealousy cause us to do some terrible things. But God is perfect. His jealousy causes Him to show His love even more to draw us back to Himself. And one day He will destroy sin which is the thing that seperates us from Him and we will never be in danger of being seperated from Him again.
I wish that day would come soon. In the meantime I come close to God everyday, swim in His love and try to stay as far away from sin as I can.
God loves me, just as I am, and He is working to take the sin out of me so I'm not tempted to leave Him.