Ovid, Metamorphoses 1.470-74. Cupid = Eros = Kama. See wikipedia.
Cupid's cult was closely associated with that of Venus; in fact, his power was supposed to be even greater than his mother’s, since he had dominion over the dead in Hades, the creatures of the sea and the gods in Olympus. Some of the cults of Cupid suggested that, like Mors/Thanatus/Letus, he was the son of Night (Nox) and Hell (Erebus), and that he mated with Chaos to produce both men and gods.
He is frequently invoked as fickle, playful, and perverse, and thus often depicted as carrying two sets of arrows: one set gold-headed, which inspire love; and the other lead-headed, which inspire hatred.
His twin by (Freudian) affinity would be Mors or Letus/Letum, i.e. Thanatus [Thanatos], god of non-violent death. (He too is the son of the goddess of night, Nox [Nyx; see (Hesiod, Theogony 212, Homer, Iliad 14.250, Pausanias 5.18.1, Seneca, Hercules Fur. 1068] or Nox and Erebus (Hyginus, Preface, Cicero, De Natura Deorum 3.17); strictly speaking, he is the brother of the personification of sleep, Somnus [Hypnos].) In Roman sculptural reliefs, he was portrayed as a youth holding a down-turned torch and wreath or butterfly (symbolising the soul of the dead).
See Freud on Thanatos (a.k.a. destrudo or mortido), a fundamental death instinct or drive that counterbalances the instinct or drive of beings to do only what they find pleasurable (Eros, a.k.a. libido), and by which organisms are driven to return to a pre-organic, inanimate state; this is an entropic principle (entropy being the idea that nature tends from order to disorder in isolated systems; entropy = a measure of disorder, multiplicity, or unavailable energy). It manifests itself as destruction or aggression, self-directed (masochism) or otherwise (sadism).
See also Statius, Thebaid 5.155ff.:
"When Somnus [Hypnos, sleep], shrouded in the gloom of his brother Letus (Death) and dripping with Stygian dew, enfolds the doomed city [of the island of Lemnos], and from his relentless horn pours heavy drowse, and marks out the men. Wives and daughters are awake for murder . . . they fall to their horrid work [murdering their husbands in their sleep]."