I [28M] discovered some messages on my fiancée's [24F] phone, and I'm uncertain about how to proceed.

I've been with my fiancé for just over three years now. Early on in our relationship, I discovered that she was messaging other people. Since we were still getting to know each other, I didn’t think too much of it at the time and chose to continue dating her, although it did leave me with some lingering trust issues. Fast forward to last summer, when we got engaged. Overall, I felt that our relationship was strong, and we were mostly happy together. Like any couple, we had the occasional disagreement, but nothing major. About a month ago, she had a night out and came home quite drunk. I picked her up, and after the usual aftermath of a night of drinking, I noticed she was unusually anxious about her phone. She left it in my car and began to panic. Instinctively, I felt something was off. After she fell asleep, I checked her phone, which I usually wouldn’t do, but my suspicions had been stirred. To my dismay, I found messages to someone she had previously slept with. She had changed his name on WhatsApp and hid the chat. I also saw messages with her football coach. While she insisted they were just friends, it felt like there was more to it. The messages with the 'ex' upset me the most. When she woke up, I confronted her, and she broke down in tears. We had a heated argument, and she moved in with her parents for about five or six days. During that time, she came over to see the dogs we share and expressed how sorry she was. She revealed that she had been struggling because this person had 'groomed' her when she was 15 or 16, and she learned that he had done the same to another girl. Although their conversation initially addressed that trauma, it shifted to more sexual topics. She didn’t initiate the sexual conversation, but she also didn’t put an end to it, which I found incredibly disrespectful. She reassured me she would never meet him and that she’s been dealing with long-standing trauma. When she learned about the other girl, it resurfaced a lot of old feelings for her. She said that someone who hasn’t experienced something similar wouldn’t understand—something I readily admit I'm not fully able to grasp. For me, messaging someone with whom I had a past relationship, especially in a sexual context, feels unacceptable. She wants to change and is considering therapy to help her through this. Now, almost a month later, I'm trying my best to make this relationship work, but I can’t help but wonder if I’m simply being foolish for giving her another chance. I’m deeply in love with her, but I worry about the long-term implications of this situation. I’m not sure I can regain my trust in her after what happened; thinking about those messages still hurts a lot. I feel like committing to her now makes it much harder to walk away compared to a month ago, and I’m reluctant to share this with family or friends because I feel embarrassed. I could really use some anonymous advice on what to do.