is it possible for a person to be your everything, but you may or may not love that person?

if it's possible, why is it so? how can one be everything but the starting point isn't love?

then, what is love? how do you know you love someone? how can you tell the difference between like and love?

how do you differentiate love and companionship?
do you love cause you need? or do you need cause you love?

life is full of unknowns and questions.
but who can provide the answers to all these?