Definition: “One that is false to the bed; one that ranges or swerves from one bed to another.” (Samuel Johnson, A Dictionary of the English Language, 1755)
Bedswerver appears to have come from the fertile pen of William Shakespeare, who may or may not have coined the word (we have no evidence of it being used prior to its appearance in the Bard’s Winter’s Tale). It did not gain much traction in the language in common use over the next few centuries. However, lexicographers have long had a soft spot for Shakespeare, and so have included words from his works even if they lacked currency. Samuel Johnson entered the word in his 1755 dictionary, from where it was copied into the dictionaries of Thomas Sheridan (1789) and John Walker (1791).
One of the few non-lexicographic works in which bedswerver does appear at this time is, oddly enough, Joseph Neef’s 1813 treatise The Method of Instructing Children Rationally in the Arts of Writing and Reading: “She told me weeping and groaning that thou art a bedswerver.”