Thanks for the replies. I will try to wait and see what will happen, and maybe forget about all of this in order to start feel safe again in that house.

What surprises me is that I noticed recently, that couple of times when I was in the bathroom, she opened the door of her room, stood there and listened silently for couple of seconds (maybe to check whether I am in the bathroom, so she can avoid coming across me) and then closed the door. She does that silently so that I can't hear it, but I do and it really creeps me out. I was thinking about talking to her about that, but I am afraid not to trigger another conflict.

She also comes back in the house every night at 1 a.m (probably catching the last bus from uni) and she again does it slowly and silently, so she doesn't wake me up. As good as this sounds, I just WANT to be woken up, so I can be....alert when she comes back at the house.

I have a dumbbell which I occasionally lift, so I started putting it in front of the door to lock it...just in case (doors of student room here in the UK don't have locks I think).

I really don't want to move out of this house. I like it here. Most of the time I am alone in it (I work at the uni during the day and I am all alone at night) and I love having the whole house at my disposal. But in that rare moments when both me and her are in the house (mornings) everything feels...a little bit creepy.