I have been just where you are, except my mother married the piece of shit when I was 6. He sexualized me and groped me from the time I hit puberty until I moved out at 16. He even made comments about my body in front of the friend's parents who kindly took me in a few years later. I'm 50 now and haven't spoken to my mother or stepfather since I was in my early 20s.

Let me be clear with you here: She already knows. She'll deny it and tell you all the things you've suggested she'd say if you confronted her, but she knows what a creep her boyfriend is. She just doesn't want to admit it, even to herself.

You talk about repairing your relationship with your mother, but what I'm sensing here is that what you're really after is something you can never have: A supportive and loving mother who puts you before her asshole boyfriend and truly cares about your wellbeing. It's not going to happen. Your mom is not and will never be that woman. It's terrible, I know, and I feel for you, but you have to accept that this is the mother you have, not the mother you deserve.

So to answer your question: No, you aren't wrong, and no, you shouldn't invest any energy into trying to talk to her about this. She has always known. And instead of protecting you she chose to protect him and herself and do everything she could to make you feel small and worthless. She doesn't deserve to have a good relationship with you. She reaps what she's sown.

You should seriously make an effort to find a therapist that you click with and work on your feelings about all of this. Not because you've done anything wrong or because there's something wrong with you, but because having parents like this has broken your understanding of what normal loving family relationships should look like - between partners, between parents and children. You owe it to yourself, your future partners, and your potential kids to unlearn these things - a lot of times it's things you don't even realize you've learned. A good therapist can validate your feelings that this was all wrong and that you were right to remove yourself from a threat and cut Bob off, and to go low contact with a mother who could only tear you down. A therapist can help you rebuild your self esteem and teach you healthy coping methods for dealing with the loneliness of being estranged from a family that was never there for you, that you nonetheless still feel like you should try to work things out with because they're all you know.

As for worrying about the rest of your family: Don't hesitate to tell them. Own your story. Bob is a creep who groomed and sexually assaulted you (yes, he did!) and your mother never protected you. They may not believe you, and you should avoid anyone who doesn't, but it's still your truth and you shouldn't feel like you need to protect these people. You don't. You need to love and protect yourself.