I need food, water and shelter. My life is more meaningful with someone to share it, but to think I can't live without a particular person has a pathetic quality to it. And "I don't want to live without you" has a trace of stalker in it. Like "if I can't have you, one of us has to die." I suspect that these imagined terms of endearment are uttered in times of crisis: during an argument or some other heat of passion.
I can't imagine sitting at lunch, picking the olives out of my salad and having my beau utter that he can't live without me. Again, I would chew the aforementioned olive and reply, "I'm sure you can."
So you are caught up in the middle of a love affair and feel the need to utter the ultimate compliment. How about, "I thought I was doing just fine all these decades, but my life is so much better since you came into it." I personally would consider it a great compliment if someone said, "You know, diva, I could live with you." That means you accept me. And as anyone who has been in a long-term relationship knows it takes a real love to be able to be in a relationship on a day-to-day basis. "I can't live without you" sounds all romantic and dreamy, but it is truly a bigger compliment to say that, with all your quirks and faults, I still could be with you every single day of my life.
It's an old saying that actions speak louder than words. But the truth is that a well-timed compliment does much for holding a relationship together. Usually the compliments are pouring out like a faulty faucet in the beginning but taper off after a sense of security envelops the relationship. It could be something that only has meaning for the two of you. Everyone once in a while I try to tell my man, "Hey, I'm not sick of you yet." That may not sound very romantic to most. but my man knows that's the highest compliment I am capable of giving.
The final word: Don't be clichéd. It's not just that I find "I can't live without you" scary as well as inaccurate. But it's also totally clichéd. Find your own words to express what you're feeling. You don't have to use big words or be as eloquent as Shakespeare. The one you love, however, does deserve to hear something from your heart, something that flows naturally from your lips and really expresses what you feel.
You'll be surprised how a meaningful few words can go a long way toward bonding a relationship.