An open mind can see how words mean different things at different times.
The word translated as jealous, for example in Galatians where it is listed as a sin, means one thing. And we all know what it means; it is a negative emotion because someone else owns something we would like to have ourselves.
But the word translated as jealous, for example in Exodus 20:5 means something different.
Suppose that you witnessed a man stealing a loaf of bread from a starving child. If I said that you were a jealous witness you would not likely be very familiar with that use of the word. But the situation is not at all about you being jealous about something you want for yourself. It is about you being jealous about something that rightfully belongs to the child rather than to the theif.
Yes, God is a jealous God. People rightfully should only worship the God who created the Universe and not any other false God. Worshiping false gods is misplaced worship and should be jealously discouraged.
Don't believe me? Do you think I have stretched this? Here is line number four from the online dictionary of the definition of jealousy:
"4. Vigilant in guarding something"
So yes, God is a jealous God and He should be.
