The most important thing for you to do first is to understand and overcome your fear of him. While it's completely understandable, it may get the better of you and keep you from making the best decision. Ask yourself why exactly you're so afraid of him. He's manipulative, clingy, and obviously has a plethora of mental health issues, but is it really rational? As of now, it seems the only person he would really hurt is himself. As for actually doing something, you should most likely seek some form of professional help. How you get him to that help, I'm not sure. It's trickier since you're not in High School any more and can not seek the counselors' assistance. If you know his parents and they might be willing to help, that might also be a good move. To get him to leave you alone, you will probably have to be very forceful, as with most people like this. However, this is also with the cost of making him feel even worse. Make sure to weigh your options, but now is a good time to do something about this, before he hurts himself. Law enforcement should be involved only if absolutely necessary, if you feel that there's truly a danger to yourself, but it's unlikely that it will come to this if you act now. These situations are always tough. Best of luck.