An Etymological Dictionary of the German Language/Annotated/Buhle
Buhle, masculine, ‘lover, paramour,’ from Middle High German buole, masculine, ‘near relative, lover, sweetheart’; likewise Middle High German buole, feminine, ‘lady-love’ (Old High German Buolo, masculine, as a masculine name only); the implied correspondences in the cognate Teutonic dialects are not recorded. It is scarcely disputable, however, that a primitively German word lies at the base of Buhle. Since Bube in Up German dialects signifies ‘lover’ also, it is perhaps connected with Buhle, which may a term of endearment formed from it.