I prefer happy endings too, but I still really liked this one. It might have been open ended, or a straight out bad end, depending on how you see it, but regardless of how you choose to interpret their relationship in the end, I think that in terms of character development, it was simply a good end. I'm very happy with how the main character turned out. Actually, I don't remember the details, but I recall her being a nicer person in general, really appreciating the other girl and valuing their friendship. Mc is annoying at times, but that's from seeing her behaviour from a detached perspective, a lot of the things she does or says is pretty common among teenagers her age, it's like, "normal", though not less annoying and cringe. And then in the end, her behaviour is just so much more likable, we see how she's grown. Even if she never directly confesses to her, even she legit keeps this inside forever, meeting that girl has changed her. That girl gave her friendship, love and warmth, and she's grown, she's happier, she's a better person now, and I can live with that.
I don't think/rmember if they ever mention it, but tbh I hope she dumps the shitty boyfriend, would have been better if she did. Hope she at least opened her eyes on wanting to date better people