Why is charlie and Alice's relationship so hard in flowers for Algernon?

If you know the plot of the story, you known that Charlie Gordon had been mentally retarded and then received an amazing experimental surgery which gave him not just normal intelligence but that of a genius. He had never learned any of the social graces however, so while his intellect was high, he was not certain how to express himself romantically.

He fell in love with Alice, one of his teachers at the night school he had been attending, but their relationship was awkward: Alice knew about the surgery, and she could also see that Charlie had no idea how to have a "normal" relationship. Worse yet, his intelligence kept increasing, and soon he was far ahead of Alice, the woman he previously admired and looked up to. I am not going to spoil the ending, in case you haven't read it, but let's just say their relationship was doomed from the start, even if they both cared about each other.