Hi I'd love some help and support.

TL;DR Told mom Im an atheist, kinda upset.

I was talking to my mother about Christmas and it led to me taking the chance to come out to her and tell her I'm an atheist. Once she asked and clarified that I do not believe in Jesus or god she seemed upset. Far more than I anticipated. Her initial response was that it sounds very arrogant. And she said I would have a sad life if I didnt have a god. And she went on asking me things like, " So you dont believe in heaven or hell after death."

Overall afterward she seemed colder, and sad, but tried very hard to seem ok with it. I told her I didn't want her to be sad or angry. And she said "Im not Im just furious. Then she smiled and said she was only kidding. Except I could tell shes not. Im nervous and afraid, and I couldn't explain why I am an atheist.

How do I answer the question,"Why don't you believe in god," delicately?