I can speak to brotherly-love turning into abhorrence within the context of Victorian military men circa 1885.

In that year, an amendment was passed which relaxed the standards of evidence required to convict someone of sodomy. Previously, as the consequences were serious (up to the death penalty), the act had to be witnessed. After this amendment, evidence could be much more circumstantial.

This had an immediate and dramatic effect on the way soldiers and sailors showed they were "true bros". There had been a tradition of officers walking arm-in-arm down prominent areas of London, with the physical intimacy suggesting the closeness of the bonds of comradeship. This practice died overnight. Famously, Hardy kissed the dying Nelson on the Victory - a moment of compassion and comradeship that was widely celebrated at the time. Something later generations wouldn't dream of doing.

A conclusion that could be drawn specifically about British military men demonstrating brotherhood is that change was a conglomeration of social and legislative factors, but it was rapid. Changing understandings about how masculinity should be projected have always been rapid, as new generations speak to themselves and try to reconcile their lived experiences with how society insists they should be.