Would you go back to dating someone who you who left you for their ex and did not say anything about it when they came back?

I(26m) dated a girl (25f) who I meet on hinge app for about a month and a half. We were going on dates hooking up and talking everyday until one day she just went cold on me, got very flaky and texting became little to non existent. After not seeing each other for like three weeks we made plans to hang out and she nails on me saying “something bad happened.” The next day she told me the move on and I did. I have a hard time getting over her because I felt like we had something good going and kind of turned into a good relationship. A few weeks later I realize stalking her social media (which I shouldn’t of done) but saw she got back with her ex boyfriend. Four months later and now she reaches out to me saying she made a huge mistake when she was seeing me and is sorry. I really miss her and want to see her. However, I feel like I’m her back up plan because it didn’t work with the other guy. She still hasn’t mentioned she had a boyfriend since she saw me last. Do I move on or give her another chance?