My 18-year-old girlfriend has been dishonest about her body count for months. As a 19-year-old, should I consider breaking up with her?

We began dating when I was 16 and she was 18. She was my first girlfriend and my first intimate partner. I knew she wasn't a virgin, but I was fine with that. However, I made the mistake of not discussing her past relationships until we’d been dating for a year. When we talked, I shared that I had only experienced talking stages before her. She revealed that she had been with four partners before me. I found this concerning, especially given her young age, but I loved her and decided to continue. Unfortunately, the thought stayed on my mind for the next six months, eating away at me until I eventually looked through her phone. I realize I violated her privacy, but in doing so, I discovered evidence of at least two additional sexual partners (including videos of her with other men, which was deeply traumatizing for me). This meant she had been with at least six guys by age 16. One of these partners was someone she had mentioned to me, claiming their relationship was only platonic; the other was unknown to me and occurred just two weeks before we got together. I also found a secret Instagram account where she followed all her past partners and even deleted recent messages from one of them on Snapchat. There was also another guy she had only given oral to, but she continued to follow him a year into our relationship. I stayed quiet for about two weeks before confronting her. The confrontation did not go well; she denied everything until I showed her proof. This situation hurts because we have previously argued about my past relationships, and she would get upset with me over my talking stages. Knowing she was angry at me while lying about such significant things is painful. It's hard to comprehend how she could maintain such a big lie for so long. Despite this, we've continued dating, and we haven’t really discussed it for the past month and a half. This is tough because I’m finding it hard to let go. I consider her my first love, which shows how deep my feelings are. However, the body count issue has been bothering me daily since the confrontation, affecting my mood and even causing me to cry at times. During this past month of avoiding our issues, we’ve shared some good moments, but some arguments have arisen, primarily from unaddressed concerns. Despite her dishonesty, I must say she has been nearly the perfect girlfriend in many respects. She hasn’t even changed her password after discovering that I went through her phone. Still, the situation weighs on me every day, and I fear that resentment is building, which could lead to future arguments if we remain in this relationship. I worry that I’m not mature enough to move past this easily, but I’m also afraid to end it because I genuinely believe we have something special. She is willing to work on rebuilding trust and proving her loyalty. Should I let this go, despite my compromised morals, or should I hold on and try to repair the damage?