What is it that makes your sister think you had a choice in all of this? Why is it up to you to yell and scream and be aggressive with your ex? If that's not who you are or what you're about, what would that have accomplished?
I think your sister is wrong. I think this is your W's choice and her's alone. I think you did what you knew to do and that's how it goes. There isn't any more should have or would have that would make a difference.
I can tell you from my experience, having done many of those things on both sides, that it makes no difference if you're a raging animal or nice as pie - can't make 'em do anything they don't want to do. If you could, you wouldn't want them in your life most likely
AJ
"Our lives begin to end the day we become silent about things that matter" MLK Put the glass down... "Yesterday I was clever so I wanted to change the world Today I am wise, so I am changing myself."