Is it normal to live like this?

Basically I have been brought up with my mum going through these "moods" some worse than others, ranging from getting in a mood and making nasty comments if me or my dad has more dinner than her, to threatening to jump off a building on a family holiday.
I wasn't usually a target of these moods, although sometimes she would tell me she rang social services on me because my room was messy.
When I was 18 I got a boyfriend who she took a disliking to, she blamed all my health problems on him, I was born with kidney failure, managed to get his number and spam text him the word "killer" over and over, and also when he came to visit me in hospital she punched and kicked him, spread round the family that me and him were on drugs, which has never been the case.
She self harms and says its my fault, and my dad is too scared of her to do anything, or just says theres no point in doing anything and "she'll be fine tomorrow"
She is also such a lovely woman and good mum when she is in a good mood so i always feel guilty when i talk bad of her but I am constantly treading on egg shells because tiny things make a huge mood, like she didn't speak to me or my dad for a few weeks over something that happened between them 20 years ago.
I had to tell my parents that me and my boyfriend had broken up just to make it a bit calmer and now I have to meet him secretly, lying about where i am and who im with just to see him, and cant see him for longer than a few hours. I know if I tell her she will go absolutely crazy, she used to tell me she would rather go to jail for killing him than have him around.
I dont want to break up with him hes the only person I can talk to about anything without worrying, but this is exhausting.
I dont have a clue if this is normal or if i should just carry on like this?
Ive lost friends over it as they dont want to see me or she just gets in too bad a mood if i mention their names, same with my dad hes lost his friends over it too
I've tried to get help for it before but then when she gets in a mood again she tries to make me write letters to people to say i've made it up
I don't think she means to be nasty i dont think she can help it.. im thinking of moving out but i feel too guilty even thinking about it
is this normal?