Final answer:
The Irish actor and activist that Yeats fell in love with was Maud Gonne, who influenced both his poetry and political activism.
Step-by-step explanation:
The Irish actor and activist that Yeats fell in love with was Maud Gonne. Known for her beauty and radical political views, Gonne was a muse for Yeats' poetry. Their relationship was complex and largely unrequited, as Gonne was more dedicated to the Irish nationalist cause than to any romantic relationship with Yeats. Despite her rejections, Yeats proposed to Gonne several times over the years, only to be turned down. She had a significant influence on his work and his involvement in the Irish nationalist movement.
Learn more about Maud Gonne