Surely the fall is more because he is sexually attracted to Ginty - or distracted by her, perhaps. One gets the feeling that his real friendship is with Nicola and/or Peter all along, and Ginty is basically a distraction that he knows, deep down, isn't as real as what he has with Nicola, but he's at that age and can't quite help himself. Plus Ginty having a massive crush on him doesn't help, either.