If you have your own room I would stay in there and do your own thing. If this person keeps harassing you, I believe you can call the police??? Have you called their non-emergency phone number? Tell them the situation, get their feedback, couldn't hurt, ya know?
Just want to throw out there that while you asked your friend if you could stay with her and she said no, remember that she has that option.
Can you go some where for a while, grab a cup of coffee, water, the news paper and just chill? Yes, you'd have to go back eventually but I'm sure you are absolutely going nuts for some peace of mind right now. I am totally feeling your pain.
I was married to a horrible roommate, lol!!! We're now divorced, I do not live under the same roof as him and it's the best thing I've got going for myself, my sanity and absolutely my sobriety. My heart goes out to you.
My best to you. :ghug