If my ex-boyfriend refuses to move out of the house I own, what legal steps do I have to take to get him out?

You need to file an ejectment action, which is essentially an eviction action for non-tenants. (This assumes your ex-boyfriend is not a tenant--that is, that he does not pay rent or have a lease; if he is a tenant, you would need to evict him for good cause, such as nonpayment of rent or on 30 days notice if he has a month-to-month lease). First you would give him notice that he must leave; however, with guest (a non-tenant), you do not need to give him any extended notice period, but can file for an ejectment action as soon as he refuses to leave when you tell him to. It would be best to hire an attorney to do this for you--not only will the lawyer know the procedures and court rules, but it will be less "personal" and the lawyer can act as a buffer.