A Romance of Wastdale by A.E.W. Mason

The strain upon Gordon's nerves had become intolerable. When he first mounted the outhouse roof he had been wholly absorbed in the horror of his conjecture that Hawke's midnight visitor was the girl to whom he was betrothed, and the need of either verifying or disproving it was the one thing clear to him amid the turmoil of his brain. Of what the visit might actually imply he took no thought. Now, however, he knew; the interview which he had witnessed left him not a glimmer of doubt.

But during the two years of their engagement, Kate Nugent had so grown into the heart of his life, had become so real a part of him, that she was not easily dethroned from his respect. He clung instinctively to a vague hope that there might have been some compelling cause of which he knew nothing to account for her subjection to Hawke. That this subjection meant treachery to him, treachery of an unpardonable kind, whatever its cause, he realised in a way, but as yet did he not feel it.