mom won't listen/doesn't get it

[Hawkest Sevrae]

Up until a while ago I would confide just about everything about my relationship with my mom, but now, after one slip up on my part that I'd rather not go into detail on, she's pressing me to break up with my boyfriend, something she promised she'd never do if I ever had a relationship. I threw that in her face but she just didn't listen. The promise was made years ago, but apparently she's bent on breaking my trust for her. Granted I lost a lot of her trust with my slip up, but it didn't warrant her breaking the promise she made. I don't want to not trust my mom, but she frankly doesn't get how much my boyfriend means to me right now. He's helping me get through a rough time, namely the slow decline of my great grandmother's health, and his support helps me alot more than just the support of my family. He's more than a boyfriend to me honestly, he's like, my BEST friend, my go-to person, my muse when I write, the inspiration of some of my best writings, and my sounding board. I've done alot to help him through his tough times, going as far as paying for a private counseling session without my parents knowing. I can't tell them that because a) I value my boyfriends trust, b) it's not their fucking business, and c) it'd give my mom another reason to press me to break up with him. Our relationship just got through a rough patch unbeknownst to my mom, and if I try to tell her that, she'll just HAVE to pry. She asked me to talk to my boyfriend and pretty much tell him she wants us to break up, i talked to him, but I left out what she wanted me to tell her. He has enough trouble just dealing with his own mom not liking him at the moment.
On any normal day, I pride myself on being a very patient person, but I've been running on thin patience, frayed nerves, stress like I've rarely it felt before, and anger for a week now, and I really don't want our talk to result in the usual scream off. On top of all that fun stuff, I've been having issues with my anemia and fighting to keep myself from resorting to self harm... I used to not get why people do it but now I can see the attraction, grim as it sounds. I have a scar from a past incident, but mom doesn't know about it, she has no idea I even cut, or may revert back to it. Honestly I don't want to go back to that but honestly I think that cold slap of reality is what it'd take to get the message across to my mom.
Any advice is welcome.

[Aletheia*]

It's hard to provide any advice considering I don't know what this "slip up" was that's causing your mom to act this way. Don't hold it all against her; you made a mistake, and it obviously is doing something to make you mother worry, and it's only natural that she'd ask you to break up with your boyfriend if he was in any way involved with something that hurt you or was involved in some way or another. It's natural to put the blame on someone else because she doesn't want to put the blame on you.

Instead of trying to talk to her when you're both upset, I'd speak with her in a calm and maturely fashion to get her to understand. So, trying to speak to her after a long day at work or school wouldn't cut it. Try talking to her on the weekend, preferably Saturday or Sunday when you're both home and can speak about what's going on privately. In a calmer setting, I'd be she'd be more than willing to listen, and to at least try to understand where you're coming from.