Good for you, Chicory! I remember when I first started setting boundaries...the A in my life wasn't a happy camper. He pushed a bit harder and louder and longer and got meaner. I distinctly remember a particular moment when I was holding fast to a boundary and he got right in my face and yelled at me. Then he stopped and said , "You aren't doing this right. I say THIS and you always say THAT. Then I say THIS and you say THAT. Then I do this and you do that and it's done! Why aren't you doing your part?" Gads our interactions were that predictable. I had changed the steps to our dance and he didn't know how to handle it!
My point is, don't be surprised if your A pushes a bit harder as you begin to set your own boundaries. I had a habit of giving in, so mine expected me to give in if he got louder - just like I had done for years. It took some work for me to be able to hold to my new boundaries. I learned to pretend he was saying "quack quack quack" instead of talking to me, and I bet I said the serenity prayer a hundred times a day for awhile.
Hang in there. Boundaries allow us to take care of ourselves. It's good stuff!