he's just looking out for his own you cant blame a person for caring about his or her family he's deff going about it in the wrong way though.. but im pretty sure from what you said his intentions are good even if his actions are misguided.. just do your best to keep it from him if he's 18 he should be moving out soon any way.. but i would play it safe and try and dig up some dirt on him to use in case he threatens you with the parent thing again hope it works out for ya'll