Basically, I am friends with this guy (i also work with him) and he won't stop trying to have sex with me. It is getting to the point that I am almost scared to be around him alone.
The bigger problem is that I have a boyfriend that I would never hurt. I have told this guy numerous times that I will not and never will be with him, but why is he still trying? And how do I make it completely obvious that he needs to leave me alone because I am truly scared.
This guy doesn't sound like a friend. If you're truly scared of him, you should _never_ talk to him in person, on the phone, or the internet. Block his email account.
Tell him you don't want him in your life. When there are other people around who'll see it, tell him STAY AWAY FROM ME! Yell at him! If you're not used to being strong, practice with someone until you're able to look them in the eye and be ANGRY and confident.
If this guy behaves like this at work, report him for sexual harassment.
If he continues to contact you, call the police and report him as a stalker.
Well telling him off isn't going to do anything for you, but telling your supervisor will help. Why would you call him a friend? Seriously, tell someone if he is bothering you that much. Forcing sex is dangerous and tell your Parents. Telling your boyfriend sounds like a bad idea. You need to tell an adult.
If he is bothering you at work, tell a supervisor or someone in charge, I would consider that to be sexual harassment. I would also explain things to your boyfriend if you haven't already. I wouldn't be considering him a friend, if he scares you!
If you're not comfortable with that, get up in his face and tell him NO MEANS NO, and that if he makes one more attempt, you'll castrate him with a butter knife. That should do the trick!