This story is told in Ovid's 'Metamorphoses' (3: 410-613). Narcissus was a beautiful youth, and Echo the nymph who loved him. Narcissus did not return her love, and as his punishment, Nemesis, daughter of Night and an avenging deity, caused him to fall in love with his own reflection in a pool. He suffered from unrequited love in his turn, and finally pined away, to be turned into the flower that bears his name.
Echo had offended Juno by delaying her when she was attempting to spy on her husband Jupiter's amorous play with the nymphs. Because of this, Juno condemned Echo to repeat only the last words spoken to her. She too pined away, leaving only her voice behind.