Bound for life humanoids

I'm creating a species of humanoid creatures that live their entire life in couples.

From birth to death, they are bound emotionally, they work together as if they were only one individual but they are actually two, and need each other to survive. For some reason they can't survive if they are more than 20 meters afar from each other, after a few days they die.

So how does that work if we exclude the use of magic? Why would they die if they don't stay together? And why would such inconvenient feature evolve?

Edit: Since they are bound for life it is more logical that they are siblings

posted almost 7 years ago

Evi‭

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