I think the answer to this is pretty obvious. Most people who read Plato seem to read him as philosophy: that is to say, their reading focuses on the ideas put forward by Socrates and his interlocutors. I read Plato this way myself when I was reading him within the institutional setting of the university. The important thing was to know what Socrates had said, and to analyze his ideas as ideas. A particular set of mental tools are employed in this exercise. The mind seeks a certain level of coherence, it demands a high standard of evidence, and it parses text as a series of propositions, syllogisms, and conclusions which it judges according to the laws of logic. Fair enough. According to this sort of reading, the question of Socrates' sexuality is ambiguous. He certainly talks about homoeroticism: he describes how a young man should deal with the homoerotic advances of lovers, exhorting his listeners to Platonic friendship and to the contemplation of Beauty rather than the satisfaction of their libidinous desires. His second speech in the Phaedrus would seem to suggest that he had some personal stake in this discussion, but then it is in the context of a demonstration concerning the art of rhetoric, and Socrates himself seems to feel that the speech is somewhat fanciful when he is discussing its relative merits with Phaedrus. The Symposium presents a similar problem; Socrates criticizes the encomiums of the other attendees, and then goes on to present an argument which he claims to have had from a woman, Diotema. The fact that Socrates appears to have gone to this women in order to get spiritual advice, and that the advice given concerns the love of boys might not mean anything: perhaps he was simply styling his own discourse to the purposes of the gathering, which seemed to be primarily concerned with male love. Certainly, nothing is proved beyond a shadow of doubt. The question must remain open.
I'll grant this. From a purely philosophical point of view, acknowledging the risks of applying a modernistic hermeneutic to texts that are significantly culturally removed, and taking into account the inconclusiveness of the considerations outlined above, it is certainly possible, but by no means certain, that Socrates may have experienced some degree of same-sex attraction.
But there is another way of reading Plato: as literature. A literary reading of the Phaedrus and the Symposium leaves the question rather more settled. The literary reader does not merely ask “What did Socrates say?” She asks, “What sort of character is Socrates? What was Socrates like?” She naturally pays a great deal more attention to the bits of text that seem extraneous to a philosophical reader: the section of the Symposium where all of the other guests complain about Socrates' long-windedness, the bit where Alcibiades twits Socrates before he tells his story of the philosopher's marvelous sexual fortitude, the squabble with Phaedrus about whether Socrates will make a speech or not, and the part where he insists that they had better keep discoursing for fear that the grasshoppers will laugh at them if they take a nap. She tries to picture the attitudes, the characters, the personalities, the sarcasms, ironies, jokes and emotions of the various speakers. I would like to suggest that such a reading answers the question with a resounding affirmative: Socrates was not merely familiar with the attractions of homoeroticism, he was sooo gay. I invite you to try the experiment, and see if you do not come to the same conclusion. Indeed, this aspect of Socrates' personality seems to leap from the page with such vibrancy that one is forced to wonder why such a concerted effort has been made to argue that the matter is ambiguous. Why deny what seems the most reasonable, obvious and natural interpretation of the text?