People who grow up in dysfunctional families are given a set of broken tools for communication, cognitions, interpretations, management of stress & other challenging emotions, and of course our ability to trust each other.
A lifetime of poor modeling made our tool kit sadly lacking in effective, compassionate, supportive, and healthy skills and behaviors with which to go out into the adult world. The older we get without having help to address this, the more our broken tools produce painful experience upon painful experience.
When we adult siblings find our relationships just as dysfunctional with each other as we were brought up to relate, it isn't a "fault" that would be the appropriate word. Two unhealthy people with heaps of unhealthy/painful/dysfunctional memories have no appropriate tools to make things different today.
That's not a "fault" so much as a tragic consequence which negatively affects our lives in all realms. Such a scenario as you present above isn't at all unusual for those of us raised with a broken tool kit. How could it be any different? Heaping guilt upon ourselves for using broken tools which don't work well isn't going to help us feel better, nor change how we relate.
The only way to pick up better tools and learn how to remove the ones which are unhealthy is to go through cognitive restructuring over a long term therapy. Meds can't replace broken tools, but they can help us be strong enough to endure the painful work.
I have learned to have compassion for myself, and as a result, compassion for my siblings. What chance did we ever have to be healthy and supportive of each other when the abuser in our home turned us against each other every day of our lives?
Instead, in a situation like this, I'd take it as a sign that my sibling is not the person I can go to for support with any real expectation of receiving it. I'd start looking around for the supportive people in my life now, and begin asking them for help with such things.
Part of my recovery has been learning that my siblings aren't abusive out of a desire to hurt me, though they may think so. They're wounded, just as I am. Our relationship was malformed and twisted from the beginning. If I expect a miracle that we all are magically cured and can have a healthy relationship, I am setting myself up for disappointment and hurt feelings.
I had to adjust my expectations to what is, rather than what I want. I'm still angry and hurt at many things, but I can see where they got those behaviors from.
Find people who are validating, and go to them for validation. Healthy people almost never bring pain and distress into a relationship, and if it happens, it's rare and steps are taken to make amends.
Stop blaming yourself, and comfort yourself. You didn't know what was going to happen when you went to him for help. Now that this has happened, have compassion for you and take steps to ensure you won't put yourself in a position where it can happen again.
