Never forget that Plato's mentor was Socrates. Never underestimate the life-changing effect of Socrates on Plato.
In the Phaedrus, when Plato talks about the relationship between mentor and mentee, he models his discussion on his relationship to Plato. (Consider how much like Phaedrus young Plato was likely to have been!) For Plato, time to talk with Socrates must have been both the most exciting and the most terrifying time of his day. He could not wait to be with Socrates, to be talked to and talk to him, and yet he also knew Socrates to be his judge, so to speak. And this is not because Socrates spent his time passing judgment on Plato, but because Plato had internalized and continued to internalize Socrates as his model, his ideal--and each confrontation with that ideal left Plato aware of some still uncorrected or some newly discovered deviation in himself from Socrates.
I do not know if many of you have had a mentor, but, if you have, you should have experiences like Plato's to draw on and to make intelligible Plato's seeing of mentor and mentee under the concept of 'love', of the 'erotic'. Speaking for myself, I was very lucky in my teachers, and can count a number of mentors. But first among them for me is James Haden, who was my philosophy professor my freshman year of college. Jim was a big guy, in his early 70's, white-haired and white-bearded, wearing heavy glasses, and he represented all that I wanted to be--embodied my aspirations. I couldn't wait for his classes; I found reasons to hang around to talk with him (or, if lucky, to walk along with him as he headed home); I looked for him when I crossed campus. My pulse rose when I saw him--even across campus. I loved him. (Is there any other way to say it?) I wanted nothing more than for him to think that I was succeeding at philosophy, nothing more than for him to make me better at philosophy. We lived out our relationship in a mutual love of wisdom.
He took a special interest in me. He was willing to delay his retirement until I graduated. He sought me out. He invited me out to lunch. Had me to his house for bacon and onion pizza. When I dropped out of college (long story), he kept in touch, wrote me faithfully. Visited me. When he died, about 6 years later, he left me his library.
I venerate his memory. Our relationship, obviously, involved no sex. But to say that the relationship lacked an erotic dimension is clearly wrong. I was in the presence of someone who participated in a mystery I wanted to participate in, and who radiated the reality of that mystery to me. He saw something in me, something, well, worthy--something worth developing. And I needed him to develop it: such things develop in an apprentice only under the tutelage of a master. To use an image from the Phaedrus: I was moulting, itching and sore and restless, overburdened by a desire I really did not understand how to satisfy. He had suffered from that desire too; he had found a way, if not of satisfying it exactly, then of living well while in its vise. I loved him for what he loved and knew how to love. He loved me for what I loved but did not know how to love. --As with Jim and me, so with Socrates and Phaedrus, Socrates and Plato?