You can’t have a healthy relationship with someone who isn’t healthy. Your mom has made systematically bad choices in her life. She has been complicit in the abuse, abandoned her boys, remarried the man who abused her daughters, marginalized your needs and feelings, and continues to negotiate her life using the defense mechanisms of denial and minimization.
Your mom doesn’t have much to offer as a parent. Her actions, decisions and behavior point to someone who act in a ferociously self-absorbed manner. She also doesn’t seem like she has the capacity to take real responsibility for her choices and their impact on you — and it doesn’t seem as if she has sought therapy for healing herself. It isn’t possible to have a healthy relationship with someone who has become the product of these very poor choices.
Yet, I do believe there is something you can do on your end of the relationship that may help. I think there are two other features that may be cultivated. First, I’d encourage you to nurture your own self-compassion for growing up with an abusive stepfather and a negligent mother. Compassion for yourself is important in evolving a compassionate stance for your mother, which I believe is what can allow you to have a civil and respectful relationship. Your mom’s way of being required that you cultivate a type of detachment from her rather than engagement. The main tool in this detachment is a compassionate stance toward her, which evolves from a compassionate stance toward yourself.
Being compassionate and nurturing your own well-being is an ongoing process. You are treating yourself in a manner similar to how a best friend would treat you. Love, encouragement and support are the messages you’ll want to give yourself. There are many techniques for developing self-compassion and this link will take you to a brief video on the bottom of the homepage that can guide you through an exercise to enhance and facilitate self-compassion.
Secondly, once you’ve been able to cultivate self-compassion I would encourage you to work on detachment. In 12-step programs, this is often referred to as detaching with love. This practice unhooks you from looking at your mom for comfort, relationship, or improvement. It allows you to acknowledge and accept who she is without trying to change her, but also without you making great efforts to help or develop the relationship. Detachment means that you stop going on the rollercoaster ride of your life is tied to hers in terms of your well-being. By turning your attention to self-compassion and compassion for her circumstance and life, you release yourself from the need to expect more from her than she is capable.