Blended family needs advice

My (43m) fiance (40f) and I both come into this relationship with boys. Mine just turned 9 and hers will turn 11 this year. They are close.

We started living together in November and my son, in his feelings, has felt unhappy because he says she does things that annoy him like entering his room without permission. Constantly arguing with me to the point he feels like he needs to defend me. Yelled at him in anger because she was mad at me from arguing. Protecting her son, but not him from arguing. He made it a point to say “she said please stop arguing infront of my son, but never please stop arguing infront of him”.

He understands adults sometimes argue, he says his mom and stepdad argue too and it’s not a big deal to him. He says it just feels bad that she shows her love more to her own son than to him.

The big incident that happened was, my ex wife told me that he had told her that he feels neutral about her and doesn’t love her because he doesn’t feel like she loves him. It was so we could fix that but it’s a private conversation for our FYI. I told my partner so she is aware and can do something about it together. I came up with a plan to sit down as a family and ensure him that she does love him and that if he ever felt like she didn’t that she was sorry and then we went around to say 2 things we love about each other. We did that and I thought that was it. We could slowly fix this.

instead while I was in a zoom meeting, she started asking him what he said to his mom. That his mom said this and that. I pulled her aside and told her “i thought i told you that was private, you’re not supposed to let him know that you know”.

i went back into my zoom calls and again while I was busy I could hear her again doing the same thing. She did it 3 times while I was busy working. I got really upset to the point of yelling. My finance then sends several texts to my ex wife saying my son said this and that. My ex wife was furious. One for breaking trust, two for trying to rub it in her face like she’s a liar. She demanded I bring our son back to her immediately and had forbid her from seeing him. So now when I see my son, which is 3 or 4 times a week we sit in my car or a restaurant for about 6 - 8 hrs before dropping him back off to his moms place. My ex wife says she does not feel safe with our son around her and says its emotional abuse.

my fiance thinks our son is just spoiled and my ex wife is crazy. She won’t break up or move out but also won’t get help. She drinks everyday, excessively like 10-12 shots of vodka a day. She says she is getting therapy but I hear her talking to the therapist and she only mentions the bad things she thinks everyone else does and not her own actions.