Bringing up breakups isn't a bad thing. You can learn a lot about someone from the way they talk about their exes (somehow, the nice guys with tragically crazy exes always turn out to be red flags). And then once she brought up his ex gf, she realized they both probably still had feelings for each other. I get why she helped him get back together with her, I wouldn't want to date someone who's still hung up on their ex either. Plus the guy was extremely nice and kind so you can't help but want to help him. As for why she felt bad, that also makes sense. Ultimately, her shot at moving on from her feelings has failed, and even though she had just met this guy he was quite the catch. Kinda like "oh I'm glad I helped him but damn he was kinda an ideal boyfriend, and now I'm still stuck with my feelings for my crush." The only thing that seemed unrealistic to me was the confession, but eh shoujos tend to have moments like these.
But yeah, rather than her being stupid, aren't you just inexperienced with dating and talking to guys? Because helping someone get back to their ex while on a date can definitely happen under the right circumstances, and asking about their past relationships is quite normal I'd say.
HOW STUPID IS THIS GIRL?! IS SHE FOR REAL?? first she goes out with a guy on a DATE and what does she do? start talking about his ex-gf and starts rambling about that his ex maybe tested him and i dont kknow what and then she helps him write a message to his ex and what happens? they get together. and then she was suddenly alone and feels bad because they got together and goes shopping instead and what heppans then. she meets HIM the blondie, and she tells him "i like you, i like you" and then asks him to reject her?! like what the fuck is wrong with her? forget that he is an airhead, what is she? complete stupid omg never seen a character being so dumb before. and this was just in 1 ch, i don´t even know if i could read the rest.