The implicit assumption that it's the boyfriends that would be doing the startup and the girlfriends that would be sleeping alone in bed - the implication that obviously it would only be that way around.
It said "a few girlfriends" for carp sake. A few. Not all. A. FEW. The poem doesn't even begin to imply that it would only be that way around. The only thing obvious here is that some people are hell bent on finding injustice hiding behind every word. I feel sorry for those people. :(