Jealousy

I remember talking with a someone and I jokingly told him that he was too jealous. He quoted Exodus 20:5 and Exodus 34:14.

"Thou shalt not bow down thyself to them, nor serve them: for I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me;"  (Exodus 20:5).

"For thou shalt worship no other god: for the LORD, whose name is Jealous, is a jealous God:"

(Exodus 34:14).

This leads me to ask

1) Is it okay to be jealous at any point?

2) If yes, when is jealousy healthy? When is it considered a problem?

3) If we agree that jealousy can be a problem, what can we do to address the root of jealousy in ourselves? How should one deal with a jealous relative, colleague, friend or fiance?

Please share your views. Scriptural references are very welcome.