My best friend was raised believing in Santa, as I was, but had a totally different reaction when she learned the truth.
It didn’t faze me in the least.
She was devastated when she learned there was no Santa, not because he didn’t really exist, but because the people she loved and trusted the most had lied to her. She could not fathom why they would lie to her like that.
I was disappointed for a while but I got over it in time. Eventually I took it as a part of growing up. Christmas over the years of my life has changed in various ways. It’s still enjoyable and a good way to celebrate the birth of Jesus.