Looking for advice after my mums cheating

Hello, this is my first time posting here I'm really hoping for some support and advice please

I am in my 30s disabled and autistic and live with my parents who've been married 40 years. My mum started having an affair over a year ago with a man my parents met and became friends with at a festival. My mum who Ive been very close to my entire life became like a different person, there's so much I could type here but I don't want to make this post 100 pages long. But there were so many lies it's been traumatic. Over the course of the year theres been 7 times where I've found out it's still not done and she promises to me and my dad it is and this time is different and the cycle continues. This man tried to be like a dad to me too, and I feel like I got manipulated at the start too

I feel like I've been living in hyper vigilance this entire time and I'm on constant watch for danger. not to go into private details but I know he isn't a good person, he's highly manipulative and I've done a claires law on him. the longest stint we had of everything being 'ok' was 6 months during that time I have absolutely fallen appart, cried most days and been so panicky that this safety isn't real and it's only a short while till it comes out again it's fake, and it did a couple of weeks ago, she's still texting him. She's gaslit me so much when I've known theres something wrong, looked me in the eye and promised I'm safe to relax and all is okay (being disabled and living at home during this has been so intense, my care and home is currently dependant on my parents so I've felt very helpless). I bet she's reasured me like this over 100 times, her words now mean absolutely nothing.

So we're onto the 7th go.. me and my mum went to therapy the other day but the therapist wasn't great, she clearly sided with my mum and didn't see an issue with what was going on 'to the point my mum was even like wtf no I've hurt my daughter' it was bizare, we're not going back but looking for another therapist. it keeps coming in waves, yesterday I felt very chill and happy and like things were settled, then today she was on her phone I wasnt intending to look but walked behind her and she was texting someone and instantly closed her phone and I'm just like oh god it'll never end will it, I tried to ask for reasurance and she just said 'do you think I'm that stupid' and she'll say 'I'll do anything to fix out relationship' she's said this every time and I say well to fix it I'd like for our relationship to not have lies. I feel so parentified it's insane and my dad is just so sad and then not a good talker which fuels my mums frustation with him more. I believe she'd lie to a therapist to get me to calm down. I am so exhausted and I just want my mum back and to feel peace and safety at home.