Ghost In My House

Ok, I was in my house one night and my boyfriend at the time left to go to work. He left out the front door. Then a couple of seconds after he left, I heard someone come back into the house through the front door and go up the steps. I called out his name and he didn't answer. I went upstairs and he wasn't up there. I sat back down. I heard this thing go up and down the stairs all night, and I just sat there, scared. It didn't leave until my boyfriend came home. I didn't know what it looked like because there was no shape to him. I could just hear footsteps on the steps....