Resentful stepmom

I don’t even know where to start & im going to try to make this short so A LOT of details will be left out. Please try hard to remember that & much of this is a rant to get the feelings out. I’m sad, broken hearted, stressed, have severe anxiety, overwhelmed...

i have been with my husband for almost 4 years. My step son is almost 7. My husband has had full custody since long before I came in the picture. Bio-mom has been in & out & very inconsistent. Well from the beginning when she found out about me, she’s had an issue with me. She never cared or tried to get to know me. Instead immediately went to making my husbands life hell, taking him to court. She even kidnapped their son which caused the courts to put her on supervised visitation for almost 3 years. It’s been hard watching her make false accusations about me & saying nothing but lies. But despite that last year after she was switched to unprofessionally monitored visits and was allowed to start calling him a few times a week, I decided to try to extend an olive branch in hopes to move forward in a positive way. It went well & she even said she would only communicate with me. But in late Feb when she found out my husband finalized the judgment documents for court she told me she would be opening a new RFO to get custody unless we agreed to give her full custody & my husband get visitation. Since she didn’t get the answer she wants she went back to her old hostile ways & not co-parent at all. It’s been so stressful. Her hostility has only grown more & more & I know for a fact she will be taking him back to court. There are moments that this situation alone with her makes me want to leave. All her poor decisions & trauma she’s caused their son has been difficult to deal with. I have been the one there, taking care of him & getting him through it on top of dealing with his constant bad behavior. We have 2 kids together under the age of 2 & i can’t deal a lot now. I find myself less & less tolerant of my stepson & the difficulties of his behaviors & how much of it is rooted from her. A lot of people tell me to detach & disconnect myself from it & just let my husband deal with it but I can’t seem to do that. I feel shitty for even feeling these negative feelings but I can’t shake them. I also know this is what she wants. She wants to destroy our home. I’m just at a loss.. advice & support would be much appreciated. Thank you for reading my rant.