Hello, Vada Dagon, welcome to the forum.

Thank you for sharing "The Lake Isle of Innisfree," as I, too, have always admired this poem, finding some of Yeats' work a little difficult to understand, but very enjoyable, nonetheless. His ability of learning and expressing such intelligence seemed immense, to say the least, and he probably writes of more symbolism in his poetry than most poets, especially of his era.
I did a little bit of research to answer your question, and could not find the most satisfying websites, but a few that offer slightly more in-depth biographies that may help.
This site always seems worth trusting, and offered some decent information, and
this site also had some good information, specialized in Yeats symbolism, but some of the writings seemed slightly . . . biased.
If you really want to go that extra mile for researching Yeats, I highly recommend reading
Axel's Castle: Study in the Imaginative Literature of 1870-1930 by Edmund Wilson, offering lots of symbolic studies on William Butler Yeats, James Joyce, George Eliot (Mary Ann Evans), Gertrude Stein, and Marcel Proust. I have yet to read it myself, but others have strongly recommended it to me - perhaps worth looking into for your research.
Good luck!