Need a perspective on how to tackle this

After being in a serious relationship for months, my gf talked to her ex behind my back but confessed to it the next day and (as per her) nothing serious happened she just told him as a final reply that she's in real love with someone else (me). Later after a lot of fights she confessed that she did delete some of his chats and showed only normal ones. She confessed to asking him "Will you wait for me if I come back". She asked him that. And the reason she gave was "I was just curious it was nothing. I have no feelings for him whatsoever" I need to know the truth, no matter how hurtful it is. Does she still have feelings for him or was she just being sympathetic as per her own words? He's the same guy who caused a lot of problems in our initial stage of relationship and she promised me any text from him and she'll immediately inform me. Still this happened and Idk what to make of it. P. S. I don't use reddit much. I am sorry if I posted this in wrong sub