Scary Building 2

I was reading some stories from across this site and I read one about a black apparition and I then remembered something that happened to myself.

I wrote an encounter about an abandoned building and this is what happened near that building before the other encounter. I don't know how I did not remember it at the time I wrote it, but I think that it is an important detail.

So for the ones of you who did not read the other story, I am going to describe the building. It is a three floors building that was used for practice and belonged to a college in my town. It is now closed, but me and my friends broke into it and encountered a strange noise.

One night, we were hanging out and the place was the back yard of this building. We were standing there chatting and at one moment I remained with my boyfriend and the rest of my friends went to a shop to buy something to eat and drink. It was completely dark, no electricity around, no cars, nothing that could have made a shadow. At one point, I stood up and my boyfriend grabbed me in his arms. I was looking directly at him and I don't know why but suddenly I took a step back and looked at his feet. Something completely black, darker than the dark was behind him. As I slowly looked up, this black mass seemed to leave and at one point it disappeared. All this time, my boyfriend kept asking me if I was okay. I had some heart problems and noticing my weird behavior, he probably thought that I was not feeling well. I looked at him, turned around with my back at him and started to cry. He took me out of that place and I calmed down. I told him about what happened and he laughed it off so I just got mad and went home.