When my mom confronted me about being gay while dringing down the highway at 100 mph i found it upsetting that my secert was out. she didn't kick me out, or make me feel bad. i was scared and felt violated much like you do. I think its not because she knows your gay, its that she violated your personal space to begin with. things wioll get better. trus me
Half of the problems between my mother and myself arose from two things: 1. She was hurt that I wasn't "completely honest" with her, that I had kept secrets from her. It wasn't so much about me being gay (although that has also been an issue), it was about me not letting her see a big part of myself. 2. I felt violated and oppressed within the actual situation itself. I felt powerless, and it made me very angry.
Space/Distance helps. Claim your space. However you can do that, anyway.
And JB's right, it will be ok.
P.S. I only read the title story of that Forster collection. How are the others?
Don't worry about your mom. Things will be fine. Just remeber: what doesn't kill you makes you a bitter, but somewhat wiser and improved version of yourself. No worries:)