Sorry Ill try to make this detailed but short as I can!
My mum and stepdad have been together 18 years, married 2017. After they got married my mum's MH got worse (she's always had bad MH due to bad upbringing/had me at 16 etc.) and she ended up going into the priory for a month, she was heavily medicated and when she come out she wasn't the same, she started an affair with another man, was taking my little sister's to meet this man and his kids behind my SFs back. I then found out and confronted her and told me SF, although he kind of thought she was as she had kicked him out for no reason. My mum then started acting 15, she was leaving my 14yo sister to babysit my 7yo & 12yo sisters all night or coming home with random men and her friend who was encouraging her to do this. It had a huge impact on our relationship and we didn't talk, she banned me from the house etc but would text me randomly at 1am in the mornings sometimes saying she was going to attempt suicide but would lock herself in the house with my sister's and a few times my partner had to break in and she was normally passed out drunk.
After about a year and a half of this she decided she wanted to sort her life out, went back into a rehab in Scotland for a month (this was paid through my SF private health care btw) and him and my mum got back together. However the man she had an affair with stalked us all for about a year after, leaving my mum's underwear on her car sitting outside the house and following my sister home from school, but my mum never told anyone until about 6months later she got drunk and told me.
Fast forward 7 years, her MH is still up and down and she drinks excessively and hides it which makes her moods worse. Her and my stepdad marriage is up and down and his MH declined too a lot leading to a drug problem last year.
Well a few months ago, she kicked my stepdad out again after they was constantly rowing, for him to see her a week later with the same man she had the affair with last time!!! This caused a huge row, with them both screaming at eachother Infront of my sisters, my mum then packed a bag and left. Broke her phone so no one could contact her. Eventually a few days later I found her at her friend's house, I tried to confront her in which her friend called the police on me. She then got in contact with me and said she was going to sort herself out but she wasn't upset about the way shes acted or made me and my sisters feel, just blamed it all on our SF and how she hates him blah blah
She said she would stop contact with the guy she had the affair with and stop drinking.
Well she hasn't stopped drinking, but two weeks later decided she missed my stepdad and stupidly my stepdad has gone back to her!!!! And then she told my little sister's to lie to me and not tell me they was getting back together!
I confronted her again but she turned it all on me and said I make her feel bad and talk to her badly and hold too much anger. She only really talks to me now regarding my son, and I feel too guilty to stop him from seeing her as they have a good relationship but I am not over what just happened, neither are my sisters but we get made to feel bad for approaching them about it.
I just don't know what to do. Sorry I don't know if anyone can even offer any advice on this or have been in a similar situation. I am just drained from it