I found an easy technological way (but not psychical one), how to leave Facebook:
1) Go to Facebook (maybe, the las time :))
2) Find "Account Settings" in the right upper corner
3) Click "Security" in the left upper corner
4) In the window "Security Settings" find "Deactivate your account" - the small link after all the links, klick
5) Explain FB, why you are deliting your account, fill in check boxes, click "Confirm"