Can I stop him/her from harassing me?

If you feel you are at immediate risk of violence as a result of harassment, then you should call the police. 

It is possible to apply for an injunction called a Non-Molestation Order under civil law.

A Non Molestation Order is a Court Order to prevent your current or former partner, or other family member, from using or threatening violence against you or your children.

It can also prevent your partner or family member from intimidating, harassing or pestering you or instructing anyone else to do so. A Non Molestation Order is usually granted for a fixed period of time for example six months, but can sometimes be granted for an indefinite period.

If you are in immediate danger, an application can be made to the Court on the same day without your partner or family member being present. This is called a Without Notice Application. The Court will need to consider whether or not you are at risk of significant harm and if the Court grants a without notice order, you will have to return to Court for a full hearing once the other party has been served with notice.

You may also apply for a civil injunction against the other party to prevent him/her from persisting with the behaviour under The Protection From Harassment Act 1997 where a criminal prosecution isn't appropriate or there is insufficient evidence to pursue a criminal case.