My reading is your second paragraph - that it's a bit of a sexual double-standard, and worrying he is a bit too conservative and not good at managing the latter socially. It's all very well for Mr Merrick to cavil at Vatican II, but he deals with the public side, while Patrick is being martyr-boy at school far beyond what his parents appear to expect. A quick fling with a sophisticated French girl who won't be interested in him as a serious prospect is much safer, in a way, than a serious interest in Ginty.