When I was a junior in high school I met a girl and we will call her "Jane" to protect her privacy. At the time we were talking via IM and the like. Long story short, we ended up dating.
She was a believer as well. Myself, I believed but needed proof on everything. I got my proof in the end. Jane was plagued by night terrors. She would wake screaming that a creature was after her. She would call me at night (we were teenagers and did not live together) and tell me that it was after her. The creature would crawl through the hallway of her home in her dreams, slowly stalking her. Sometimes as she walked through the hallway and would see a dark mass in one of the rooms. Like it was waiting on her. Having not experienced it myself, I could only comfort and calm her.
One night I was over at her place, we were laying in her floor. Why I cannot remember, but we were a odd couple to start with. We were watching a movie, she had dozed off laying on my arm. Jane said she slept better around me. As the movie ensued I felt fingers run up my leg. I went to take her hand until I realized I was still holding her hands as she often slept this way. The fingers stopped at the end of my thigh. I looked around as best as I could without waking her and saw nothing. Not wanting to alarm Jane, I kept it to myself nor wanting to think about it. I did not like being touched and the fact that I could not see what it was did not help matters. So I buried it in my subconscious and moved on.
Jane's night terrors grew worse. She would run through the house screaming. At one point she attacked her stepdad as he tried to wake her and blacked his eye. She does not remember any of what happens during the night terror, merely the dream itself. Being chased by a black creature was all she could remember. We end up breaking up on unrelated terms and we lose contact.
Six years later we reconnect and start dating again. Things go smoothly for about a month until one day while I was at work. She had gotten into a domestic with her mother and begged me to let her move in with me. I agree, and while I finish my shift, she gathered her belongings and waited for me at my place.
The following two months were rocky. She was different somehow. Paranoid, aggressive and scared. At night her night terrors tormented her. The screaming and clawing were becoming a usual occurrence. She would accuse me of cheating. While I was at work she would hear voices throughout my place. Footsteps at the front door. We ended up having a messy breakup in the end. I had to kick her out after she put one of my guns in my face.
The following morning I awoke to loud heavy footsteps coming down my hallway. I jump off the couch, grab one my pistols thinking that someone had broken in through the back door. The footsteps stop short of the living room. I carefully walk over, ready to fire. Break-ins were all too common where I live and I was not taking a chance. I round the corner but see nothing. I go room to room shouting at the individual to come out but find nothing, the back door still dead bolted along with the front door. Nothing ran by me and I searched every inch. It had vanished.
A few months ago I was moved to 24's at a different station in a nearby city. It was one those days too; everything was going wrong. Typical Monday. My partner in the evening could not come in until 11:00 or so. I decided a nap was in order. I hated waking up early and had not been sleeping well. The footsteps awoke me again. This time it sounded like it was directly behind me. Thinking my coworker had arrived, I turn over on the couch. Groggy, I raised up and called him a creeper for watching me sleep. No response. I looked around the station; I could not find anyone. I called my dispatcher to check and see if he was just screwing with me, hiding, waiting to pop out and scare me. However, my partner was still on his dayshift and on a call.
My dreams started getting more violent and gruesome when I can remember them. I cannot help but think that my ex's spirit has found a new playmate.
I have worked with children with mental disorders like ADD, ADHD, etc. If you still have contract with your ex girlfriend, I suggest getting her check out because a lot of what you described are associated with mental illness (I'm not saying that it happens every time but the numbers are up there). If you can't get her to go then I suggest talking to her mother, relative, or friend.
Good luck and keep us posted.