Love, National Gallery, London

Love seems a theme more suitable to a poetry anthology than an art exhibition, so it's fitting that the first item on show is Tracey Emin's embroidered, partly illegible love poem, sprinkled with appliqué roses: "Those Who Suffer Love (I'm OK Now)". Heartfelt, skew-whiff, hand-made to the point of being rubbishy, it's disarming and directly tackles the theme. Round the corner, things get a bit more complicated.

Vermeer's Young Woman standing at a Virginal features a painting of Cupid holding up a playing card, a glyph of fidelity. The chair in front of the woman is empty; she looks expectantly at the viewer. It's a painting of suggestive absence. In Raphael's Madonna of the Pinks, Mary gazes down fondly, the sturdy Christ child looking back with an altogether more complicated expression of foreboding. Next to Mary is a sinuous Cranach Venus, stark naked save for her glorious pom-pom hat, ignoring poor bee-stung Cupid. The label informs us that this painting was in the personal collection of Adolf Hitler.

The facing wall is all about gesture: Joseph Wright of Derby shows us a married couple, she on horseback, he with his hand flung negligently over her knee as if to say, "I own all this." Stanley Spencer's ugly lovers have outworn beauty and youth but caress each other tenderly; Hockney's male lovers clumsily grab against the wall of a urinal, their teeth clashing. Their bodies, in fudgy pinks and browns, resemble the love affair of a Fab lolly and a strawberry Mivvi.

Crepuscular blues, and arum lilies among the red roses, give Marc Chagall's Bouquet with Flying Lovers a melancholy air and with good reason: the painter leans out of a window to embrace his dead wife, flying through the night, softly enveloped by her white bridal veil. Holman Hunt's virtuosic Isabella and the Pot of Basil is another portrait of a recently dead wife, but it's about as moving as an Arts and Crafts furnishing catalogue. The lustreware pot in which Isabella has buried her lover's head is particularly desirable. Further along, Dante Gabriel Rossetti's Astarte Syriaca is fit for the altar of a satanic chapel; his Middle Eastern goddess of love is a menacing and muscular presence, like a shot-putter with PMT. Facing her is Frederick Sandys' golden Medea, an icon of jealousy as she curses the thread that will kill her rival for Jason.

Possibly the weirdest picture here is Murillo's John the Baptist: a fluffy lamb places its hoof on the forearm of a winsome, ringletted boy who awkwardly makes his upward-pointing gesture with the other hand as he clutches the beast. Its sentimental message ("Your Saviour wuvs you!") is horribly undercut by its painterly brilliance. Elsewhere, Hendrick ter Brugghen's Jacob Reproaching Laban for Giving Him Leah in Place of Rachel is a sprightly and attractive rendering of a typically sordid Old Testament episode.

In Tiepolo's brilliant oil sketch, Cate Blanchett as Cleopatra holds up the pearl she will dissolve in wine and drink as Anthony looks on in admiration. The stallion barely restrained by its handler in the lower left corner makes the point explicit, as does the cat licking oyster shells on the floor of Jan Steen's superficially innocent Interior with a Man Offering an Oyster to a Woman. The most intriguing pictures here make up their own story rather than illustrate scenes from the Bible or mythology: Amrit Singh's jewel-bright girl getting ready to meet her beloved beneath a portrait of a henna-tattooed Madonna, or Goya's A Picnic, a strange and sinister rural scene involving drunkenness, male swagger and a curiously blank-faced doll.

But to complete the experience, take in Bronzino's Allegory with Venus and Cupid, surely the most complex, sensuous and cynical image of love ever painted.