In Stanley Kubrick's film Barry Lyndon, there's an scene where the title character's mentor, Captain Grogan, is gunned down by French troops. As he lies dying he asks Barry to "kiss me, my boy, for we shall never meet again." The scene is all the more affecting for its empathetic recognition of the historical gulf between modern and 18th century notions of male friendship, which prompted me to wonder how these notions differed. (Notably, in the same movie, there's also a scene where two unnamed British officers bathe naked in a river together and declare their love for each other without implication of a romantic connection.)
This article (a PDF download) states that friendship was elevated to a higher ideal, in part to compensate for the partial breakdown of class and customary relationships, as well as to take up the emotional slack in societies where upper-class marriages were defined by expediency. As such, male friendships in the upper classes could incorporate emotional declarations we moderns might associate with passionate romance (or Romanticism), and practices we might otherwise perceive as frankly homoerotic. (The article is on the German states in particular, I'm primarily interested in Britain and France but am assuming for now that there's a continuity.)
But apparently there were limits. In the same article a pair is mentioned who shared "too many kisses to escape slander, suspicion and mockery." Considering this, and contemporary legal and religious practices, it seems clear that a strict line was drawn between ebullient male friendship and romantic or sexual attachment.
My question is, basically, where was that line drawn?
In 1700s Europe, what practices were considered acceptable among male friends that today we would probably consider homoerotic? In what contexts were such practices (in particular kissing) considered appropriate, or even obligatory, and when were they proscribed? And what role, if any, did class, education, or social allegiance play in all of this?
EDIT: A little research has turned up mixed but mostly negative information. This (frankly delightful) history of kissing claims that social kisses between friends were popular up to the 1750s, but soon fell out of use in Germany at least. It also, under "the kiss of peace" recounts a dramatic social kiss-fest among the French revolutionaries. I've still only skimmed it. A guardian article claims it fell out of fashion in Britain by the 1700s. The article on Germany remains an outlier, and this history Reddit claims kissing remained common, but it may turn out the depiction in the movie was anachronistic.