The only talks that I ever walked away from where I felt like I had accomplished anything other than hurting myself even more than I was already hurt were the ones I had communicating the boundaries I had set for myself and what would be the consequences if and when those boundaries were crossed.
Of course, I wouldn't try to dissuade you from learning this for yourself, in your own time. It has been invaluable for me to try everything I possibly could, to no avail, so that I could learn this lesson for myself. Because I'm perhaps rather hard-headed? Except looking back I wish I hadn't WASTED so much of my life with this nonsense. Hmmm...did I just contradict myself?