I found a few articles on this topic -
This one points out that many of the portraits make you think they must have been lovers - which they may have been, but the physical closeness was normal enough that this wouldn’t have been assumed.
A couple of articles make the point that when the only acceptable physical closeness for heterosexual men becomes a sexual one with women, it stigmatises and isolates men and puts undue pressure on women (in the same way that men can’t provide all of their partner’s needs either, and close female friendships are important). It also exaggerates the importance of finding a partner when this is the only way you can express closeness in a physical (but not sexual) way.
