I feel for you, I have had to deal with a parent with a similar mindset of her against the world and being emotionally manipulative. I think I understand why you are having such a difficult time setting boundaries. You are a very empathic person and your instinctive reaction is to put yourself in others shoes and see it from their point of view. You feel sorry for your mother and while she is narcissistic and selfish, you instinctively also sense her pain and her struggle, even if she deserves that pain and even if her problems are self inflicted. I understand the pervasive guilt that comes with wanting to be kind to a person who you see is in distress.

I struggled a lot when I was trying to get away from the guilt and ranting my mother would lay on me. I'd always end up apologizing and letting her have her way because I couldn't bring myself to keep saying no to her. She'd alternate between being very accusatory (and she knew my weak points and exactly how to get under my skin) and being desperate and sad. If I ever managed to keep saying no to her I would inevitably feel sad and guilty and had a harder time believing that I was right in doing what I was doing.

It took a lot of therapy and antidepressants after my kids were born to eventually learn to enforce boundaries. What it came down to was this - my kids don't have anyone to advocate for them. All they have is me and my husband and it is my responsibility to put them first above all. Between my kids interests and my parents interests, my kids win. I still sometimes acquiesce to my mother, because that long learned habit is so hard to give up. But I have learned to stand up for my kids, because who else is going to do that? Your mother is being loud and using a lot of clever arguments to convince you, your child cannot do that. You have to be your kids champion. He can't question your actions now, but what are you going to say to him if he asks you, years from now, why you didn't protect him from her when that was your primary responsibility?