HEADHUNTERS THOSE MOFOS

So i have known a few headhunters now and know a good one is fuckin hard to find. These days ive been approached quite a few times by them and some have really peaked my interest. Which leads to me to my damn question.

Are headhunters to be trusted? Like I got my job now through one. When i want to switch should I tell them? I am afraid that they might alert hr with the purpose of refilling the same position. This will ultimately be a bitch in the case I do not secure an offer by then. Has this ever happened to anyone?

I want to tell my headhunter that Im looking to jump but you know these mofos can never be trusted!!!!!!!!!!!!!!!!!!!