There are some unfortunate situations that occur when two cohabiters (usually refers to two unmarried people) need to part ways. It is even more troublesome when one partner refuses to leave. The law in most states says that if someone has been living with you for a certain number of months, he or she has a legal right to live there---even if the person isn't on the lease or deed. You have to go through a formal eviction to remove the person from the premises.
Notify the cohabiter that you intend to evict them. You can do this by sending a certified letter to your home in the person's name, posting a note on their door, or handing the notice directly to the tenant. The note must state the date by which you want the person to leave. The time requirement depends on the rules of your state, since in most domestic situations, there is no lease agreement. It will usually vary from 15 to 30 days. Keep a copy of this notice for your records and to bring with you to file the eviction.
If your partner refuses to leave, go to your local court administration building and ask to file an eviction. It has to be a courthouse in your county. The clerk will quote you the filing fees and give you the appropriate paperwork (usually called a "Complaint for Eviction" or similar). Complete the paperwork and pay the fees (usually between £65 to £97). You can usually take the papers home with you to fill out if you need more time.
Be sure to include any rent due or damages that you are seeking from the cohabiter in the eviction paperwork. If you can prove it in court, the judge will put in a monetary judgement in addition to granting the eviction.
The court will serve the defendant (your cohabiter) with paperwork stating that they have to go to court regarding the eviction. If the tenant does not appear, the eviction will be automatic. If both parties appear in court, each will be able to argue the case before a judge.
When the eviction is granted, the tenant will have a few days (usually about a week) to either appeal or leave the premises. If the cohabiter does not leave, file a writ of possession (there will most likely be an additional fee) so that the sheriff can come to physically remove them if necessary.
File a restraining order with your local courthouse if the cohabiter is violent or abusive in any way. This will automatically evict the person, because they are unable to come within a certain number of feet from you. You have to own the property to evict someone. If you are leasing an apartment, you have to either talk to your landlord about evicting the partner, or move out early to avoid the person. If the person is not on the lease but refuses to leave your home, call the police. The officer will usually escort out the person (be sure ask the officer for any keys in the person's possession). If the cohabiter has been living at the apartment for a long time, the police may not be able to make the person leave legally, but will advise you on what to do if you want your partner gone for good. In any case, be sure to file a report with your local police department about the situation.