I wonder if a better way of saying "not one person can fill my needs" would be to say, "different people access different parts of me".
I have a penchant toward the word "need" simply because it's the language I've learned through NVC. I like to recognize which needs I am having that are/are not being met within myself when an emotion comes up. This is of course part of the process of taking responsibility for them myself.
There are needs that I cannot meet for myself. Companionship, for one.
I think "need" has become a distorted romantic way of expressing a deep connection and commitment. I would rather use more conscious language like, "I have a connection with you that is unique in my life and it's very important to me". Is there anyone in my life that I absolutely need? No, not if you consider a need life/death. Or even happy/unhappy. I would be hurt if certain people left my life, but I would also move on.
My heart is too big to fit into one person.