If you treat your romantic partner like a friend she or he will not feel fully beloved, because main expectations about love are sex and romanticism, not friendship and loyalty. If you become a friend or a sibling of your partner, most likely s/he will be looking for the inexplicable magical love outside the couple unless both of you have given up on love in favor of friendship.
Love is incomprehensible for us humans, but we have two certainties about lasting relationships: either the couple has exactly the same ideas about love, sex, romanticism, and friendship or one of them is absent-minded and the other one has an affair.
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