SOS 😭😭😭

Ok, so I have done something that I shouldn't have a few months ago and my friends and family cannot find out. If they find out My life will be altered completely and definitely not in a good way. I told a guy I thought  I could trust and he turned on me for a girl that despises me for no particular reason. She has since moved on from him but now he has started harassing me with text messages on my phone and facebook and I'm scared that he'll share my secret like he almost did before. I really need advice on what to do in a situation like this. BTW this guy has nothing to lose.Â