What is the ruling on a wife saying to her husband, “You are my soul; I cannot live without you”?

There is nothing wrong with a wife’s calling her husband “my
soul” or telling him “I cannot live without you”, in sha Allah; this comes
under the heading of kind treatment between spouses. 

If a woman says that to her husband, she does not mean it
literally; rather what she means is to express her respect and love for her
husband, just as the soul is of great importance to the body. 

The same applies to her saying “I cannot live without you”;
what she means is: I would feel so lonely if I lived without you. 

Such words are spoken without intending the apparent literal
meaning. This is something that is well known in the speech of the Arabs,
such as when they say, “May my father and mother be sacrificed for you,”
“May your hands be rubbed with dust,” and so on. 

An-Nawawi (may Allah have mercy on him) said: The words (of
the Prophet (blessings and peace of Allah be upon him)), “Shoot, may my
father and mother be sacrificed for you!” indicate that it is permissible to
use this expression. This was the view of the majority of scholars. However,
‘Umar ibn al-Khattaab and Hasan al-Basri (may Allah be pleased with them
both) disliked it, and some of the scholars regarded it as makrooh for a
Muslim to say this. 

The correct view is that it is permissible in all cases,
because it does not really mean sacrificing them; rather it is a figure of
speech and expression of love for him and acknowledgement of his status.

End quote from Sharh Muslim by an-Nawawi. 

And Allah knows best.