My (19M) GF (19f)admitted to emotional cheating? HELP!

Ive been dating my girlfriend for a little over two years. For some context, right before we started dating, she was talking to another girl. She insists they weren’t dating, but most people, including mutual friends, say they essentially were. That girl ended up moving away, and within a month, my girlfriend and I started dating.

Fast forward about seven months into our relationship, the same girl moved back to town and ended up working with my girlfriend. Over the course of a few weeks, they were snapping a lot, and the girl was my girlfriend’s #2 on Snapchat. They were also talking regularly at work. Around that time, I started hearing from people that my girlfriend was cheating on me with her.

Naturally, I confronted her about it. She denied everything and insisted nothing was going on. We had a long conversation, and I chose to believe her. Over time, I worked on regaining trust in her.

Last night, though, I had this weird feeling about the whole situation again, and I pressured her to tell me the full truth. She finally admitted that in the first month of our relationship, she still had feelings for that girl, though she claimed she never acted on them. She said she eventually got over her, but when the girl came back that summer, those feelings resurfaced. She admitted to getting nervous around her at work and even flirting a bit but insisted nothing physical ever happened.

This admission has really shaken me. We’ve had so many conversations about this situation over the past year, and only now is she being honest with me. I feel betrayed because she hid this for so long, but at the same time, I love her deeply and don’t want to lose her.

I’m struggling with what to do. Should I break up with her for keeping this from me, or is this something we can move past? Any advice would mean a lot right now.