It will never make sense
I am a BM and SM. All our family members have adjusted to our blended family situation except one, who has instead chosen to be an angry and bitter individual. After almost ten years of trying to stay positive, I will now save myself. We all need to vent and wonder, but I finally understand all the years I've spent trying to make sense of a situation that will never make any, is just time spent reliving the insults and injuries, time spent in wasteful self-flagellation. Unfortunately, this one maladjusted member has found very effective and passive aggressive ways to have enough power in our 'family' that she prevents us from being one due to her skillful and derisive nature. I am done being hurt, I am done making excuses for this person. If someone chooses to live a hateful life, I choose not to be part of it.
For those of you wondering what you are doing wrong, no one is perfect, but if you can honestly say you have been kind, supportive, respectful and not overbearing 90% of the time, the problem is not you, it is either the nature of the step relationship, immaturity on the part of others, or mental health issues in other members of the situation. If you are a future SM who thinks you are a loving enough person to do it right and not end up like me posting this in a public forum after ten years of trying, you are just fooling yourself. My non-SM friends, even the most supportive ones, do not understand. I am glad for them that they don't. A new term I just learned, "responsibility without authority" describes my situation well, mixed in with a large dose of projected hate and there you have it. I have sacrificed much to try to make things better, only for the ante to be upped constantly and for the hate intensity to increase. I am sad about the situation and always will be, but I am done putting myself in the line of fire. If I knew then what I know now, I would have RUN!