How/when did you accept they would never change?

At what point does your heart really start to believe they will never change? This is always a big fear of mine. In my brain, I KNOW he won't.. I've been through enough cycles in just the last two years to be able to predict what will happen next and the outcome is never pretty. But at the same time, my heart fears that he may actually change for the better. My ExN is back with his "wife" that he has left countless times before over the last few years, but I have a fear he will actually be a better person for her *this time* to try and make the marriage work... even though he has cheated on her continually throughout the marriage and lied and strung her along just how they all do. They have moved back in with each other after being separated and living in different states for 4 years and are "playing house" as it seems. How is it fair that he would change for her and not for me? I keep waiting to hear a piece of news from a mutual acquaintance or see something that will prove to me that he is still the same and he is no better to her than he was to me. I guess I want to know that I'm not wrong about him and he will always be a big piece of $%^&... I don't know why this bothers me so much.

I went back in the forums to read posts on this topic, and I came across one posted by a member from a couple of years ago who had just been sucked back in by her ExN and believed he really was a changed man... even though there was clear fear evident through her typing. There were never any posts that I could see from this person after that particular post, so I do not know what happened to her in the end, but I wish I knew. Reading it made me feel anxious and scared -- I don't want to be that person who gives in only to see YET AGAIN that it was just a mask. How do you accept that this person who you thought was "the one" isn't really that person at all and move on from it all?

We have no contact, but I keep ruminating over this particular thing. Give it to me straight, ladies and gents.