Song of Songs

What is a love poem doing in the middle of the Bible?

We go from reading the songs and prayers of David and others in Psalms, the words of wisdom from Solomon and others in Proverbs and the confusing musings of Solomon in Ecclesiastes to this?  It is such a departure from what I just read.  

Am I wrong, or is there quite a bit of double entendre in Song of Songs?

This is not a book of the Bible I ever read as a child, that is for sure.  I don't recall any Sunday church lessons coming from Song of Songs either.  About the only thing that seems to be in line with the previous books is that King Solomon is mentioned by name.

Was this put in the Bible to remind us that love and desire are completely normal?  

She: "My beloved is radiant and ruddy, outstanding among ten thousand.  His head is purest gold; his hair is wavy and black as a raven.  His eyes are like doves by the water streams, washed in milk, mounted like jewels..."  He: "Your hair is like a flock of goats descending from Gilead.  Your teeth are like a flock of sheep coming up from the washing.  Each has its twin, none of them is missing...my dove, my perfect one..."  She: "I belong to my beloved, and his desire is for me...for love is strong as death, its jealousy unyielding as the grave.  It burns like blazing fire, like a mighty flame..."

The words may be a bit outdated, but the sentiment is still there...love, love, love.