It's not totally healthy in this society either based on one fact: There is something about the relationship that causes them notable distress, namely that intense fear of separation. The fear is kinda justified, if for the wrong reasons, but that doesn't make it healthy.

See, romanticizing the idea of "needing" someone and "not being able to live without them" is actually a really serious problem - it teaches people to be content with sacrificing their individuality and becoming dependent, which in this or any society is REALLY BAD. Not something we want to accidentally end up doing.

These two...would be able to survive without each other for at least a little while, and certainly much longer after the outside threats are cleaned up, but the problem is they wouldn't really want to try - and no matter what Twilight says, that's bad. Unfortunately it's been romanticized so disgustingly much here that I don't know how to show that.

So even though that society that glorify stalking (assuming you mean it literally, not sarcastic opposite meaning...), they also frown on 'parasite' that cannot live independently?

It's not really parasitism and it's not about that society vs. ours. It's about fixing a serious problem in ours. They'e not parasites in regards to each other, that implies draining; they're both perfectly fine and able to have other healthy relationships as long as the other is around. It's the fact that they are as emotionally unequipped to handle separation as they are physically. No matter what your views, it's not good if a person suddenly becomes a quivering mass of goo who can't function when a person isn't around.

The problem is that they don't have an emotional back-up plan and don't really have the opportunity to form one.

... I kind of lost now...
fixing serious problem in ours?

So your aim is to show how unhealthy that kind of relationship is?

Actually, I think my question about the society of your story background have divert the original question. XD sorry, lol. But I didn't quite get it when I first read it.

The problem is the things we think are healthy in relationships. Losing your individuality, becoming a useless mess if your partner isn't around (a.k.a. Damsel In Distress Syndrome)...and for that matter, stalking and carrying on even after the unwilling object of your affection says they're not interested (even if those aren't that relevant to these two). The importance we as a society place on having a romantic relationship is WRONG. It is NOT the be-all, end-all thing that absolutely everyone ever needs or else they fail at life and we shouldn't romanticize the idea of feeling like it is, but we do.

The aim is to show two things: that yes, that level of attraction is unhealthy, but at the same time, no relationship is perfect, so if you're all happy and no one is actually abusive...YES, you should try and work out the complications, but NO, you shouldn't let it destroy you.

Basically I'm trying to show a good but flawed relationship as, well...good, but flawed.

So~ That is your underlying message, moral of the story.

Moral/message : Romance is not everything.
Aim : 1. No relationship is perfect. 2. That kind of relationship is unhealthy.
Question : How to stage happenings to express that good and flaw relationship.

First of all, things must happen. Stage one event that express the goodness of the relationship and another event that show how unhealthy it is.
To stage those events, your background and character's personality matters.

Since I do not know much of the story, I can't really suggest specific events... but, if you are talking about the balance of expressing the good and bad of relationship...
Heard of 7 point of Story Structure or something like that?
1. Hook - kinda introduction
2. Plot turn 1 - good point
3. Pinch! - bad point
4. Mid point - preparation/brewing for a big scheme?
5. Plot turn 2 - good point
6. biiiiiiiig cliff hang pinch - bad point
7. Conclusion
The explanation is how I use it though. XD

I hadn't heard of that one before - I kinda end up doing that anyway but it's nice to see it broken down.

This particular relationship is actually only going to be a part of about 1/3 of the story (sort of...the same story is going to be told three different times from three different points of view for the sake of replay value). There are two things that I know are in there that...could easily show the bad, but I'm trying to figure out how to write them well without people being all "Aww, how romantic~! <33" over what would be, without one small detail, the worst idea in the history of bad ideas that any character I have ever written or cowritten has ever had, but with that small detail it was...the right idea for largely the wrong reason. One of the main things I'm considering is having the character who did it say it like that.

You can google for 'seven points of story structure' for the video presentation and original explanation. *winks*

I am not sure how to help without knowing some details...

And I can't really give any details because they're all spoilers and everyone involved is trying to be as secretive as possible about pretty nearly anything beyond the first five chapters of the first version of the storyline. Considering that storyline's main characters' biggest mystery is who they are and where they came from...virtually everything is a giant spoiler.

The good news is, just talking about it and trying to describe it has given me some ideas, so...

That is good.
I am not intended to poke through your spoilers/secret. Just stating that I can't figure any solutions, other than telling you the strategy to tackle it. Don't feel pressured. Because I thought you actually requesting for a rather specific solution.

I find, listing out the points in point form, help streamline my thinking.
Like, you have the 'cause', so you would need the 'effect' and 'solution'.
Base on the 'cause', and on the setting & character, effect would be different.
Or you can even start with wanting to use that 'solution'... anyway, find it organize way for me to think through.