From the USA. What a difficult situation to be in. Your mother has put you in a tough spot and it seems like the best thing is to ask to have a talk with her alone and out of the house. Find a place to go to walk or at the very least be away from people. You want this to be a private conversation.
Let your mom know that her conversations are not being kept as private as they should be. Be clear that you are uncomfortable with what you’ve heard, and it makes it difficult to talk to her. Explain that you understand why she would want to talk to someone else, and that it creates anxiety in you. Don’t try to fix this, explain what you’ll do as a reaction, or minimize it. The work on your part will be when you hear your mother’s response to not lose yourself. If she says you shouldn’t have these feelings that would be a tine for you to assert that her wishing you didn’t have them doesn’t change the fact that you do.
Put the burden of what to do back on your mother. Ask her what she thinks is the best way forward. The idea here is to connect with your mom, talk about what is real, and work together toward a solution.
If this doesn’t work—or as an alternative—ask if your mom would come to a therapist with you and bring the problem there. This has the advantage of having a 3rd party present to assist.