Help her understand why I don't trust her and should i stay or go?

My fiancee recently revealed she had been in a 26 year affair which transcended every relationship since she was in her early 20's including 2 marriages.

Her revealing this truth made me recognize she had been telling me some of the same lies she had used to hoodwink her former husbands and boyfriends.

She is now hurt because I do not want to be in a relationship with her and is having a dificult time understanding why I think it would take a good while before I can trust her.

My feelings go back and forth between two (2) camps. Leave and don't look back or take some time to learn to trust her and try again.

Your thoughts on things that might help her understand why it would take a good while I before trust her and advice on me staying or going.

Do you know who she really is?

Do you love her?

No, I don't really know who she is.
I do believe that I love her, and am also willing to walk away, happy for the experience.

Is she still continuing the affair? If so, I would definitely end it.

Under which circumstances would you be willing to stay and what exactly must happen for you to go away?

She's a serial cheater, adulterer and liar. GO! Even if you love her, she doesn't love you, she loves that person she's been 20 years cheating with.

I'm... I'm a little confused about your story. What do you mean she'd been in a 26 year affair? So, for 26 years she has been consistently hooking up with the same guy regardless of whether or not she was in some other relationship? Am I interpreting that correctly? Like, over those 26 years she was in "official" relationships with different guys (apparently including 2 different marriages) but was consistently cheating on all of them with the same guy?

Was that ongoing during when you were with her as well? If I AM interpreting that correctly, then that sounds a Hell of a lot more to me like this other guy is her true love and everybody else (probably you included) is her guy on the side, even though she married some of them and never this guy. I mean, she's consistently been with that same guy for 26 years? A "fling" doesn't last 26 years.

I mean, I'm not sure if I am just misunderstanding your story, so maybe you can clarify. I'll say, though, if I did get that right....

Then, yeah, I'd agree with the others. Leave her in your dust and DO NOT look back even for a second. If that is the case, then she doesn't deserve you and probably doesn't deserve anybody. But, again, maybe you can clarify if perhaps I just misinterpreted that.