Hello leomama,
I was in DBT training for a few years as well, so I
kind of know what you're referring to. (I haven't read the Twilight books, I've seen them everywhere though.)
We need to use our Wise Mind to try to understand different perspectives of the different characters in the chain that you're referring to. It isn't easy...but, try to take a step back and identify the trigger. {it's Bella} How are you being triggered? {You're against cheating & you may view Bella's behavior as being purposely conniving or sneaky with Jacob.} Now try to look a little deeper... {How do you personally identify with Jacob? This is an important clue to you, I hope that it holds your answer/s.} From there, you have something to refer to more tangibly at your next appointment with your T, hopefully.
Very best wishes and gentle hugs sent your way...