nidan verb (lower class) with 'ru' ending (archaic), intransitive verb
to be lovesick
Archaic intransitive verb describing a state of emotional turmoil from love. Not used in modern Japanese; encountered only in classical texts.
古典では「恋い乱る」と書いて、恋に心が乱れるさまを表した。
In classical texts, 恋い乱る was written to express the state of one's heart being disturbed by love.