To fully understand this you need to define a few things. First a concept is more or less a way of thinking, which relates to things or features of things in the world. To have a concept of something is to have some kind of psychological ability to place into perspective or to “individuate”, or pick out, all kinds of things in the world, for thought and talk, and for action.
Some of our concepts are of psychological states. For example, you have a concept of pain and a concept of belief and you also have a concept of love. The suggestion that I am making is that there is a mismatch between love and our concept of love. But what is the nature of that mismatch? That’s where everyone beings to get away from the “idea”.
One possibility and the easiest one to show is that our concept of love is of something that simply doesn't exist. The German philosopher Friedrich Nietzsche took very much this line on freedom of the will: there is no such thing, he said. We mistakenly think we are free because the idea was imposed onto us by other people (the priests), who wanted to make us think we were free in order to make us feel guilty, and who wanted to make us feel guilty in order to have control over us.
Similarly, according to this view of the mismatch, we have the concept of love because of our social history. But there is no such thing as love. And, one might add as a gloss to this view, our lives would go better if we didn't think there was such a thing.
To say, baldly, that there is no such thing as love seems (if you will forgive the understatement) to be something of an overstatement. But there is another version of this view that might have more appeal: it's not that there is no such thing as love; rather, the mismatch lies in this: the concept we have of love is hopelessly idealistic, hopelessly romantic.
Before they get married, people are often warned not to be too idealistic about love so that they will not be disappointed. I do think it's true that when we are young, we often expect too much in our loving relationships – of ourselves and of others. But I don't think that many of us grown-ups have such an idealistic concept, so this isn't the mismatch that I am going to pursue here.
Science has sometimes shown us that something can be redescribed, in terms of something more basic or simple, but in a way that leaves nothing out in the redescription. For example, the kinds of things talked about in chemistry can be redescribed in terms of the kinds of things talked about in physics. This is called reduction. Consider heat. Science has shown us that heat can be redescribed in terms of, or “reduced to”, molecular motion; that's just what heat is. We have two concepts – “heat” and “molecular motion” – but these two concepts are of one and the same thing. So it would be a confusion to say that when we put a cup of soup in the microwave, the increased movement of the molecules in the soup causes the soup to heat up. Rather, the increased motion of the soup's molecules just is the soup's heating up. There aren't two things going on, with one causing the other; there is just one thing.
Sometimes, though, the claimed redescription of a psychological state doesn't involve reducing it to the terms of a more basic vocabulary. Sometimes the redescriptive claim involves redescribing a given psychological state in terms of another psychological state. For example, the French writer La Rochefoucauld claimed that benevolence or kindness to others is really just self-interest in disguise. Often – and I am not sure why this is – this kind of redescription reveals or expresses a certain cynicism – and La Rochefoucauld is a good example of this. Moreover, it's often a short step from claiming that such a redescription is true, to claiming also that there really is no such thing as whatever is the target of the redescription – benevolence in this example.
This is really elimination rather than redescription, and it often goes with a dismissive “nothing but”: benevolence is nothing but self-interest in disguise. So how would this go for the case in point? Love is really nothing but ... what? Well, in our cynical age – an age dominated by sex – I suppose sexual desire is a favorite. There is a book called Love Ain't Nothing But Sex Misspelled. Other candidates for the “nothing but” eliminative claim might be the desire for companionship, or a redirected desire for parental love. So here, unlike the first proposal I considered, the idea isn't that there is no such thing as love, or, less unconvincingly, that we have a hopelessly idealistic concept of love; the proposal here, rather, is the eliminative idea that love is nothing but some other psychological state – sexual desire or whatever it is.