As you suggest, odds are high the stepfather has internal doubts about his own masculinity/heterosexuality.

That's it in a nutshell. LW's problem is a steaming mash of toxic masculinity, homophobia, transphobia, and misogyny.

I want to steal Brice away from his clueless mother and whatever the frick LW is, and keep him safe with books and quiet indoor activities and the occasional quiet outdoor activity and unlimited and unconditional love