My girlfriend isn't loyal and keeps flirting w other guys but I can't let her go... What do I do?

This is my first REAL committed relationship. We've only been together for almost 6 months now, but we're so close and not to be cringy lmao but I feel so in love with her. It was so perfect until the third month, when she started dating some other guy without me knowing for ab 2 weeks. They never met up in person though, we're teenagers so like it was only over the phone w social media. Well I found out who the guy was and told him that we've been together, and he shows me screenshots of their texts... She denied everything until I showed the proof, then she started breaking down and crying saying she was sorry. I didn't want it to end so I forgave her. Maybe that was my first mistake. bc over the next couple of months after that, I've had about 5 to 6 different guys hmu telling me about how she's been flirting w them... I try talking to her about it but she says that she can't change... I don't know what's wrong with her. Last night I talked to her about it, about how she never really shows me off on snap or anything, and how I'm always wondering who she's talking to. I ask her to show me off and she flips out and makes me feel bad for not trusting her. Like wtf. And she won't show me off... A few days ago I saw a guy on her snap, didn't think much of it... I asked ab him but she said it was just a streak.. But after that argument, I add him on snap and he hits me up telling me that she was cheating. Apparently she sent nudes to him... Now I confronted her, ofc she denied at first but then was saying sorry ab how horrible she is... She then starts telling me that it will change from now on and that she'll show me off. Even after all that I can't find the strength to let her go, like I love her and I don't know what to do...
My girlfriend isn't loyal and keeps flirting w other guys but I can't let her go... What do I do?
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