In Greek mythology, Pan was in love with Syringa. To avoid his advances, Syringa changed herself into a lilac bush. Pan finding the plant, used it to create a pan flute to memorialise his first love. 

Victorian woman often wore lilac whilst in mourning for late husbands. 

Linked with the Alexandra Dumal novel, La dame aux camelias. The story tells of a couple from different classes falling in love. The young mans father finds out, and to avoid scandal sends the young woman away. The young man mourns her leaving after being told she has left for another man, while she falls ill and dies alone thinking of him. 

Their dropping of the whole flower can also represent a quick or noble death in Japanese and Chinese floriography. This falling together can also represent staying together. 

Apparently named after a German folktale of a young betrothed couple. The bride-to-be stopped to look at these blue flowers, so her groom stopped to pick them for her but fell into the river which carried him away.