I am a native speaker of American English and have never heard "refuse" be modified by "deeply." I looked up "refuse deeply" in Google ngram , and there were NO references to it at all. The OED Sentence cited is not on the topic of "refuse" or "deeply." Not one comment has cited another example of "deeply" modifying "refuse." Based on that, I think it fair to say that "refuse deeply" is certainly not idiomatic in American English and probably not idiomatic in written British English.
It is not true that everything published in English is perfectly grammatical. The sentence cited may well have come from a "romance novel," a type of popular fiction not generally esteemed as an ideal of English prose. To "love deeply" is a common idiom as evidenced by ngram. The placement of "deeply" appears to be one of those minor grammatical failures that native speakers manage to ignore without conscious thought. A reading that makes sense is "... pain to be refused by a woman whom he loved so deeply." Possibly the author is another person deluded into thinking that passive constructions should always be avoided in good writing.