I want to end my relationship with my Christian friends

I have 3 friends from university who are very religious, and one of them, let’s call her Anna, is especially kind and great to be around. Last year, we ate together often, our university residence was catered. At some point she invited me to her Bible studies. I was curious, since I wasn't religious at all and I never really attended church that much, maybe 9 times in my life. So I went, even though I’m an atheist. At first, I was looking forward to the discussions (especially the Q&A sessions), but I quickly realized that their answers didn’t resonate with me.

Anna is also homophobic, which is ironic because she had a girlfriend at one point but now says “God saved her.” I truly think that she's really afraid of hell. By the end of the year, I knew I wanted nothing to do with the religion, but I stayed friends with her because she’s genuinely nice.

This year, we’re in different residences, and I’ve fully embraced being an atheist. I haven’t been to Bible studies since, and I get annoyed when people try to preach to me. Anna and I still care about each other, but we don’t talk much anymore. I’m still in their group chats from last year and want to leave them, but I know Anna will ask why.

How do I tell her that I’m an atheist and don’t want to hear about her God without it turning into her trying to "save" me? I know it will be such a huge thing, and I really don't want to deal with that. I have delayed this for the entire year, and I just can't anymore. I also feel somewhat guilty cause we shared so many memories, and it genuinely hurts me to think that will just go down the drain.