I wonder what do you call two things that are related to one another in such a close way that each one "needs" the others in order to exist and none of them can last without the other one? I know just two adjectives and their associated verbs. Whilst dictionaries couldn't help me much, I wonder which choice doesn't work in this sense:
1- They are interdependent.
2- They interdepend.
3- They are correlative.
4- They correlate.
I would appreciate it if you could let me know about even a bettrthere option if exists.