Why is this so hard for me? This should be the closure I needed...?

She doesn't want you - or at least she doesn't want to be faithful to you - but she doesn't want anyone else to have you, either. You need to cut this woman off. It's clear that she was cheating or she would have no problems letting you see the phone records. If she's not into conditions, then she's not into the obligations and boundaries of marriage and you need to tell her you have no interest in her and are moving on with your life. And then do it. I assure you that you will get over her.