Gf broke my trust what should her punishment be? An when will I trust her again?

I found on a messenger (separated 2 years not legally signed yet ) she was messaging the ex husband about if he ever thinks about her cause she randomly had a thought this an that he said some dick things like ya bra bla you and your boyfriend can do this an that she mentioned how she loved an cared for me though. Which made me relieve but he said when she comes back to the state he referenced sex she was like hey cut that out! She is going back to a friends wedding. An sign the divorce papers . You don t make small talk with someone you re divorcing , she saw me flip out I said how would you feel if I talked to my ex? She agreed.I don t trust her an I am thinking of breaking up only things we agreed they talk about is the divorce an when to meet for that. So we can get this guy out our life for good an never associate again. but I am still furious. don t offer break up advice cause I told her if she is flirting or trying to make conversation again I am dumping her an she is choosing that if she did that an she agreed. an will never ever do that again she wants me and only me. But I don t completely believe that myself . I do but I m hesitant an she needs to be punished like I need to feel satisfied an not angry anymore and I am. I also will probably go to the state for the wedding to let this guy catch an A$$ whooping , she said whatever is fine. even though she s more guilty. I need her punished cause I don t trust her yet. How can she earn it.