I can't control my fantasies and it's getting dangerous.
What is dangerous about your fantasies?
I'm in constant fear of getting caught doing things I'm not supposed to be doing.
It's okay to have fantasies that are strange, as long as you can avoid acting on them in real life. If your fantasies make you feel guilty, or it you think you can't control the urge, you need talk to someone about it.
I can't talk about it, I can only act them out.
In that case you should still see a therapist.  They might be able to help you put your ideas into words, or even act them out in a harmless way.  If you do this, you'll be able to get the help that you need to control your thoughts.