Eros (erōs, Greek: ἔρως) for Lewis was love in the sense of “being in love” or “loving” someone, as opposed to the raw sexuality of what he called Venus. **Side note: Eros = root of erotic. Think about it for a second.** The illustration Lewis used was the distinction between “wanting a woman” and wanting one particular woman — your sweetheart, your soul mate, your better half. Eros turns the need-pleasure of Venus into the most appreciative of all pleasures but nevertheless, Lewis warned against the modern tendency for Eros to become a god to people who fully submit themselves to it and use it as a justification for extreme selfishness.
After exploring sexual activity and its spiritual significance in both a pagan and a Christian sense, Lewis notes how Eros (or being in love) is in itself an indifferent, neutral force: how “Eros in all his splendour … may urge [one] to evil as well as good.” While accepting that Eros can be an extremely profound experience for human beings, Lewis does not overlook the dark and sinister way in which it could lead even to the point of suicide pacts or ritualistic murder, as well as to furious refusals to depart, “mercilessly chaining together two mutual tormentors, each raw all over with the poison of hate-in-love.”
Different than friendship, lovers, “are always talking to one another about their love” and “are normally face to face, absorbed in each other,” says Lewis. The danger in romantic love is to follow blindly after a feeling of passion without being aware of the greater context of the relationship. Too often, Lewis notes (and contemporary culture reaffirms that), we celebrate the passion of our romantic relationships and think its absence means that such love has tragically and permanently died. Certainly, true romance is not so fickle or fleeting, though the feeling is useful to measure the relative health of a relationship.
As Lewis says, “The event of falling in love is of such a nature that we are right to reject as intolerable the idea that it should be transitory” and “In one high bound it has overleaped the massive wall of our selfhood; it has made appetite itself altruistic, tossed personal happiness aside as a triviality and planted the interests of another in the centre of our being. Spontaneously and without effort we have fulfilled the law (towards one person) by loving our neighbour as ourselves.” We must keep in mind that Eros is just one component required for a successful and happy relationship with our romantic partner. It has a different feel and function to Philia and Storge.