Need advice for heavy fawn response/lifelong repeating enmeshment patterns

Hi everyone, I'm (26F) here to seek some advice for my severe fawning response and share a little of my experience with enmeshment trauma.

Growing up, I had an enmeshed relationship with all of my primary caregivers in different ways. My parents divorced when I was young, and my mother remarried a man she met on the internet, who turned out to be a predator. I was put in the place of "girlfriend" rather than "step daughter", not allowed to have a bedroom door (he took it off the hinges), I had to tell him that I loved him every time I saw him or he would flip out and do things like throw all the animals outside and scream at me, call me a dumbass, shoot a gun at the ground outside to see if anyone would care if he shot himself, installed keyloggers on my devices to track everything I typed, and publicly humiliate me by recording me crying and posting on facebook how long it's been since I told him I loved him.

And for my biological father, him and I were very close, I loved him very much, but boundaries were certainly crossed. He would make inappropriate comments toward me about my body, watch pornography next to me and try to give me alcohol, and put me in the middle of conflict between him and my mom. I have messages between me and my dad when I was 10 years old, of me begging him to let my mom claim me on taxes because "otherwise we will lose the house". I didn't even understand what any of that meant at the time.

My mother is the parent who I have the longest-running relationship with, as my father passed away on my 15th birthday and a few months after, my stepfather was arrested. My mother and stepfather had a child together, my little brother, who is severely autistic and disabled. My mother and I have never been close, we never said I love you or hugged or any of that, and she made it clear to me that I was a huge burden in her life. But I was also responsible for her emotions. If she had a bad day at work, or troubles in her personal life, etc. I was immediately scapegoated as the reason for her bad mood. I wasn't able to set any kind of boundary, show any emotion (positive or negative) or make any choices for myself without it having a profound negative impact. As an adult, I wasn't allowed a lock on my door, I was bound to responsibility for caring for my younger brother and her, helping her pay the mortgage and bills when she spent all her money on hobbies, and she took all the social security money from my dad's death and had full access to my bank account so when I made her mad she would just start taking hundreds of dollars out of my account until I begged her for forgiveness and acted however she wanted me to act. I don't want to go into detail more about my relationship with her because it's still fresh.

With all this being said, I have noticed that this has impacted me so deeply to where I carry this belief that I'm fully responsible for everyone else constantly. Most of my relationships have started because a guy shows interest in me, I'm not interested in him, but when I try to reject him he pushes my boundary so I just give in and date him so I'm not "mean". This has led to me being sexually assaulted multiple times. I end up paying their bills, and providing endless emotional labor. Every roommate situation I'm in is similar. I end up taking on all of their personal issues, throwing money at them any time they ask no matter the reason, and being tasked with childcare and other responsibilities I didn't sign up for. Because I just can't say no. I've sacrificed so much for others because I just can't say no. Saying no has always led to disasterous outcomes, such as being kicked out, yelled at, sexually assaulted, etc. On top of this, I am on the autism spectrum and have a lot of difficulty understanding how to react in any social situation or when I'm being taken advantage of, and I'm so dissociated from my body and my own needs that I don't know how to recognize when I'm not aligned with or comfortable with doing something. How do I know where the line is between honoring my own needs and being selfish or ungrateful? I don't even know what I'm feeling unless someone else tells me, because every time I've expressed my feelings, they're just invalidated. I struggle with self harm and other ways of self punishment because I believe that everyone's emotional state depends on me, and if anything I've done dissapoints someone, I must be punished, and that I deserve horrible things to happen to me.

I am almost 27 years old and this specific trauma response has ruined my life. But I'm at least aware now of some of my patterns, the origins, and I'm conscious of the deeply rooted fear I have regarding becoming responsible for someone else again. My roommate is currently pregnant, and it's triggering these fears heavy. I'm terrified that I will be roped into being a replacement parent figure again like I have been so many times. I'm terrified for what will happen when my mother gets older and needs care, or when something happens to her and the full responsibility of what happens to my disabled brother gets put on me. I've neglected myself so much that I can't even care for myself very well, how can I care for him? I just want to be free. I want to worry about me and me only. I want to be a human. I don't want to constantly abandon myself over and over out of fear.

If anyone has any advice for me, please let me know. In particular: how can I recognize when I am overextending myself, and how can I manage the terror that fills me when I disappoint someone? I have a long history of my physical wellbeing and my security (aka my finances and having a place to stay) being threatened over and over for any display of autonomy or boundaries, so this is a deeply rooted survival mechanism for me. I am in therapy, but not very often because I can only afford it once a month.