Girlfriend texts a guy who flirts with her?

So a couple months ago my girlfriend went to a concert with her friend. (Let me add more info)

During this week before and after the concert me and my girlfriend were fighting about everything. We then broke up the day after the concert and we still fought. She told me there's this guy who she met at the concert, and that he has really pretty eyes. She told me they have been texting for about a week after the concert. Constantly, the guy is telling her that she's much more prettier than her friend and that my girlfriend was flawless. He even you corny jokes. During this time me and my girlfriend were just on a break. We fought about this guy and I got mad at her because she allowed him to flirt with her. She promised me that she wouldn't text him ever again.

We got back a couple days later.

2 months later I went on her phone to take a selfie just for funzies. I look at her messages and there I see that they were texting each other. The conversation was short, and they only talked about how sick and icky she was. I was fine but I kept scrolling up to see that it stopped. She said she deleted the older messages because they weren't important. She said he starting texting her by apologizing for not texting her and that he doesn't hate her. She said it was the right thing to talk to him because he was apologizing.

How could I trust her? She thinks he's hot and he think she's beautiful. I know he likes her but I don't know of she likes him. She promised not to text him.