They make an adorable couple! (I would LIKE to think that, if not for that damn warlord thing, Kes and Neelix never would have broken up.)
Sure, Neelix is a tad jealous at times, but never dangerously so. Let's put it this way: I suspect that Kes was his first love, and thus he was unprepared for a relationship and kind of overcompensated at times. Before Kes, he wasn't used to being a boyfriend and didn't know "how" to be one. Fair enough, yes?
Really Neelix was never "dangerously jealous"? What about his behavior in this episode?
http://blip.tv/sf-debris-opinionated-reviews/voy-parturition-review-6350892
When Neelix is assaulting other crew members at the slightest hint they may be interested in Kes, Neelix has become dangerously jealous.
The review was actually funny ad had some points.
However, it totally missed one of the hilarious scenes in the episode. The interaction between Kes and The Doctor in sickbay shortly after the very hiarious fight between Neelix and Tom:
THE DOCTOR: Are you all right?
KES: I'm fine.
THE DOCTOR: Are you sure? You seem a little
KES: I'm fine.
THE DOCTOR: You know, if you skip lunch, the result might be a lower blood sugar level, which could. I'm sorry. It's in my programme. I see something wrong, I must attempt to diagnose it.
KES: There are some things you can't cure. Neelix and Tom Paris had a physical fight-over me!
THE DOCTOR: How delightful!
KES: Delightful?
THE DOCTOR: You should consider it a high compliment. Throughout history, men have fought over the love of a woman. Why, I can quote you autopsy reports from duels as far back as 1538.
KES: That's not funny.
THE DOCTOR: It's not meant to be. You've always been interested in autopsies.
KES: On my homeworld it's so much simpler. You choose a mate for life. There's no distrust, no jealousy, no envy, no betrayal.
THE DOCTOR: Hmm. Your world must have very dry literature.
"Parturition" is sometimes criticized for being a dull episode. I actually like it, mostly for some of the hilarious moments in it.
As for Neelix jealousy, I do think that Kes definitely started to lose interest in him around the time for this episode.