A person keeps calling me. I am afraid of him because he tried to ruin the relationship between me and a person I like. I am afraid that he would do mean things again.
He told me when I was in love with another person that he liked me. I told him I really didn't like him.
I had to be nice to him when he called me, since I don't want him to feel that I hate him. But the things he did before make him no longer my friend.
After the first phone call, I thought that was the last call from him. But it was not. When my life is in peace, he suddenly calls me again. And sometimes he calls me almost at midnight. I even went to the counseling center to talk to a doctor for that. I don't know how to do with it. Now the person I like tells me he likes me too. I feel very happy. Although we are far away, and we might never get together, I am content and grateful. However, yesterday afternoon that guy called me again. I was very afraid. I lied him I was with my friend and had to hang up, and he asked me which friend I was with. I told him it's none of his business and hung up the phone.
What should I do? I am afraid he would ruin my dream again.

If and when he calls you you have to tell him that you are NOT interested in him as a boyfriend and you do not appreciate him calling you.
If you feel really threatened maybe you should tell him you feel he is harassing you by not letting it go that you do not want him and get your number changed.
Do not give him any reason to feel hope. Avoiding any and all small talk. Often when you get into a conversation with someone like this they take it as a ray of hope and see it as encouragement.

If he calls, don't answer, if he keeps calling, report it to the police and get a restraining order.

Thank you very much. I have thought about not answering his calls. But I am afraid that he would know that I am afraid of him. Also, I don't want him to know that I keeps his number.

I don't think he would take it as being afraid of him.
Answer a couple more times and tell him you are in the middle of something and hang up just like you did the last time and then quit answering.
Then he may think you are just always too busy.

Don't answer his calls at all and I think he will eventually realise you aren't going to answer and get bored with trying.