Flowers for Algernon question

He had real feelings for Alice. He was actually in love with her, and that scared Charlie. Fay was someone he liked, but the stakes weren't as high because he wasn't in love with her.

Charlie found it very easy to make love to Fay because he wasn't emotionally developed. Even though he became knowledgeable very quickly, his emotional status progressed imperceptibly. As you know, the naive Charlie remained in his conscious at times. Lingering there, he would become fearful because Alice was someone he sought after for a while and so it was very hard for him to make love to her. That is the reason why he wanted to imagine Alice's body as Fay's body... so he wouldn't be so anxious and fearful. Being with Alice meant a great deal to Charlie and wasn't as big of a decision to make as being with Fay. Think of it this way, would you find it easier to greet a welcoming stranger on the street, or the person you're in-love with but are unsure of where your relationship stands?

Because this is science-fiction from a man who obviously never grew up in a family strict around sex. For him, sex with a complete stranger, and a crazy one at that, is somehow so much easier than with someone you feel safe around. It's an alternative fact.