Yes, but I have no idea why some people (like her) do not use brain and they don't learn from the other's mistakes. We live in times, where knowledge is almost everywhere. Internet boosted our access to information so much, that such self-destructive actions can not be explained otherwise than by the rotten character.

She is not naive, small kid. Who normally allows others to use you like trash? She let others treat hersef worse that whore, since she does not need to exploit her body for food or money. She got nothing form this, not love, not security, not happiness, not even money or food. Who normally do such things? I do not understand it.

And this is not shown in this manga, but normally no one, especially a girl, will change so abruptly from shy to the opposite. There is a safeguard in everyone's mind against extremely destructive behavior, that's why people don't jump off the roof for any reason. If someone is raised in a pathological family then yes, but no one changes so abruptly for no reason.

If people had no brakes (like in this manga), mankind would have become extinct long ago, because there are more unhappy people than happy ones.

I agree mostly with what you wrote, but one thing is wrong. They do these things because they want to. If it were as you say, girls would see themselves only as a sex toy and nothing more. I'm not an expert on the subject, but women have more to offer than just one night sex to make others consider them human.