It is not at all unusual for someone who has been abused to feel as you do. With support and time, you can learn to manage your feelings about what happened to you and have a much happier life. However, most people do need that professional support.
Sometimes parents want to believe that leaving the abuser fixes everything. It is too painful for them to face that the children may have lasting effects from the abuse. Sometimes they have unresolved guilt that their kids were abused and they didn’t know. That doesn’t make it okay that your mom refuses to get you into treatment. But maybe it helps you have a little compassion for her.
I’m very sorry that the therapist somehow offended your mother. Please tell her that all therapists are not alike and that often people need to try out a few different therapists before they find the professional they feel they can trust.
Since your mother is influenced by her boyfriend, a place to start in this situation might be to ask to see a Christian therapist. The boyfriend may be more willing to support you getting into treatment, if he doesn’t feel like his beliefs will be challenged. Yes, I know you are an atheist but you don’t have to share the beliefs of a counselor to benefit from their treatment. Counseling isn’t about a religious debate. A good therapist won’t try to push their beliefs on you but will be more concerned with how to help you recover in a way that works for you. Once you feel better, you may be able to transfer to a therapist with more compatible beliefs if you still feel that it is necessary.
In the meantime, please consider joining one of the forums here at PsychCentral for some support from others who share your experience. You might also talk to your school counselor about whether there is a free teen support group in your area that would be helpful.
I wish you well.