You have to report this right away to human resources. Most importantly start keeping a diary of all these incidences because you may need it in court one day. Try and never be alone with this person and if possible get a transfer. Also speak to his supervisor.
Sexual harassment is illegal. If you work for a large employer, you should inform your human resources department immediately. If not, you need to document the harassment and, possibly, speak with an attorney.
What you are describing falls under the heading of sexual harassment. It is something that no company should tolerate, and most do not. If your boss has a superior go to them, and tell them about your concerns; if not, consult a lawyer.