They do it by prearrangement with themselves. They do it as a debt of honor.

他们通过与自己的预先安排来做到这一点。他们这样做是为了荣誉。

'Because you know even less of love-making and matrimonial prearrangement than I, and so you can't draw invidious comparisons if I do my engaging improperly'.

“因为你对做爱和婚前安排的了解比我还少，所以如果我的婚约不当，你不能得出令人反感的比较”。