For most people, love is a response to need fulfillment. Everyone has needs. You need this, another needs that. You both see in each other a chance for need fulfillment. So you agree-tacitly-to a trade. I'll trade you what I've got if you'll give me what you've got. It's a transaction. But you don't tell the truth about it. You don't say, "I trade you very much." You say, "I love you very much," and then the disappointment begins.