Plato was a student of Socrates.  Socrates considered writing far inferior to talk (written text was an "orphan," its "father" (the writer) not around to defend it from a later reader's mistakes in reading).  Nevertheless, Plato interpreted Socrates's thoughts in dialogues which he wrote, after the fact.  The other "biggie" of that era, Aristotle, followed Plato and "rewrote" philosophy to his view.
    In very broad terms, we can think of Aristotle as arguing from the specific to the general (induction), and Plato the reverse (deduction).  To Aristotle, we witness specific details (one white-barked tree, then another, then a third) then we make general assertions about what we've witnessed (Let's call these particular trees "birches" and see what kind of knowledge this yields).  Aristotle is sometimes referred to as the "father of the scientific method" by dint of his approach.  Plato thought that all things reside in the "ideal," and specific instances of "reality" strive toward this pre-existing ideal.  (All birches seek the ideal birch state.)
    In his famous "analogy of the cave," Plato saw humans as chained, so to speak, to face the back wall of the cave.  The ideal was behind them, but they lacked the capacity to turn around and look.  All they could witness were the shadows of ideal matters cast onto the wall of the cave,  These shadows they thought was reality, but the philosopher knew better.
    In a culture, a "philosopher" (lover of wisdom) was the person most able to perceive the ideal.  Since he was a nice guy, it was then his task to impart a yearning for the ideal to the youth of his culture.
    In The Symposium, he will make this argument.  He will also, with the help of Diatoma later on (note how, even in this patriarchy, it is a woman who has the goods about love), argue for the first time in Western thought that love is in effect an "ideal."  The early speeches hardly do this, but they do provide what notions on the subject might easily come to the mind of an educated Athenian at the time.  The later speeches, starting with Aristophanes's myth (the most popular of the speeches these days), develop more and more abstractly toward the reader comprehending this situating of love among the ideals (truth, good, beauty, etc).
    For our purposes in this class, let's try and come up with, therefore, a notion of what "platonic love" might imply.
 
About the homosexuality:

    What we would label as child abuse these days was in fact moderately accepted in those times, though not without "rules of conduct," so to speak.  The Symposium strives to define these along the way.  It was mostly aristocrats who indulged in such pedophilia (love of children), and common folks weren't always that thrilled about it.