How do I prove I trust her ..again.?

Long story short Ive been dating her/shes living with me for a year now. Shes talked to her x behind my back first lie was that she was telling him she wasnt with me and that she couldve been pregnant. She wasnt pregnant and admitted she thought she might be to me but after taking a test she wasnt. I ended up calling her x and it was not good news... he didnt even know about me.. and she had been saying so many things to him even building a future in his head.. He was furious after the conversation and they ended that segment... this was about 7 months ago. Just recently last week I noticed she was distancing herself to me.. so I checked her phone later on and sure enough he was in it again... but under a friends name.. I told her I was done and ended up sleeping in the second room. She came crying (both times) saying he called her and she wouldnt talk to him anymore. I told her I would start talking to MY X if this was the case and how she wanted it. She said no and told him the next time he called that she couldnt talk to him anymore. I would understand she wants to be friends and i told her that was fine but if she was to be friends w her X only fair i be friends with mine... Now Its been hard and a night mare woke me up ..I wasnt fully awake but she was calling and i kind of lashed out on her bringing up the past... now shes sleeping in the next room last night but came to me in the middle of the night.. she ended up leaving me saying i didnt trust her and shes tired of us both being unhappy . HELL SHE JUST STOPPED TALKING TO HIM A WEEK AGO.... AM I IN THE WRONG ? I WISH I COULD JUST FORGET IT AND MOVE ON... BUT THIS IS THE SECOND TIME THIS HAS HAPPENED I HATE IT THAT IM HAVING A HARD TIME BC I LOVE HER VERY MUCH AND JUST HOPE IM THE ONE SHE WANTS I MEAN GEEZ WHAT A WASTE OF TIME IF IM NOT... PLEASE TELL ME HOW TO PROVE TO HER I TRUST HER AFTER ALL THIS... ITS KILLING ME. OR WHAT I SHOULD DO.. MY PHONE IS CURRENTLY OFF AND I DOUBT ILL TALK TO HER TILL I GET HOME IF SHES EVEN THERE. IM IN BAD SHAPE AND ALL I WANT IS TO HOLD HER AND BE THE ONE SHE WANTS .