How can I politely ask my mom to stop posting (and other actions) on my behalf on Facebook?

About 3 years ago, due to some past actions of my misuse of the Internet (which I did learn my lesson, I promise), my mom collected my Facebook password to monitor my activity. I'm okay with this, as I don't have anything to hide anymore. However, what does bother me, is that she messages, posts, and responds to my notifications and friend requests on my behalf; without asking sometimes. Specifically, she's messaging her ex-boyfriend and it bothers me because I don't want him to think I was messaging him, when it was really my mom. (He blocked her) A little background info they were an off/on relationship for many, many years and he was a bit Narcissistic. I checked my Facebook messages and they were talking about sci-fi movies and nothing much of actual importance, but it still bothers me because I don't want to have contact with him. He sent me a friend request and I intentionally left it as unaccepted (not declining either, I didn't respond), and my mom accepted it. I deleted the posts from my behalf today (again, these weren't of much importance either, just my mom posting pictures of us on vacation, and such, but I don't want people posting on my behalf like that..), and I also deleted him from my friends list. So, how can I have a calming talk with my mom about this? I don't mind that she has my password, but I don't like her utilizing my account in this way on my behalf. I know I'm a minor, but I don't appreciate my mom doing this.. Thanks so much!! :)