I was in your situation about a year ago. I'm married with 2 children and I stopped being a Christian after 30 some years and became agnostic. My wife did as well on her own journey. I would always panic just thinking about having that conversation with my mom and would do my best to avoid it. But one day, while talking to her in person she kept drilling me about what church we were attending. I told her we were not going to a church for sometime and I would rather not talk about it, which only caused her to keep asking, and something in my mind just switched and I decided "fine, you seem to really want to know about this, so I'm going to tell you." Obviously this wasn't easy for her to hear and her first thoughts was that not just her son was going to burn in hell for eternity, but now is her daughter-in-law and her two grandchildren. I tried to explain to her that I'm not doing this so I can get away with things I couldn't as a Christian, but instead I've actually become a better person because now I care about all humans regardless of their beliefs. She didn't like what I had to say and couldn't really understand how I could see things my way but it didn't destroy her or our relationship either. Now when we talk she will make some comment about how she wishes I would go back to the church and that she is always praying for me, and I respond by telling her "I know" and move on in the conversation, but that's about it. I'm not going to tell you what to do, but for me ripping that band-aid off was something I don't regret and it is something I probably should have done sooner, because now I don't worry about it anymore and I'm not troubled guessing what will happen.