Questioning husband about cheating lasts hours.

I recently found out that my husband has been lying for over a year about his interactions with his ex girlfriend. Prior to being married he temporarily ended our relationship to be with her. Once we reconciled she began harassing me in the worst ways. Texting me from unknown numbers after I blocked her. Threatening to show up at my job or at my home. She called me names. Continued to message him. He told me if he heard from her he would let me know and he did not. I had a baby this winter and she messaged me saying she was pregnant which has now been determined a lie. She also calls me horrible names to him and he has never told her to stop. The past 5 days have been long and emotionally packed. I’m barely sleeping or eating. Sometimes feel like I’m losing my mind as I over think everything and over analyze. On a few occasions I have questioned him for close to 5 hours and he is becoming frustrated by the intensity and time frame of it. I do not do this intentionally but once I start I just spiral and lose track of time. do not want to lose our marriage. How can I stop this?