Hah, you've read too many stories with happy endings xD When a girl like Malena is already in a relationship, and stuff happens like it did, the outcome is exactly as it is. Sadly, this is pretty realistic.
As bullshit I mean her returning to that asshole. She should ditch him anyway. She didn't learn anything during that one night.
I know, that's why I said it's pretty realistic. She got swept up by her feelings, but after the 'safe zone' was gone, she couldn't do what was necessary, or at least, people who resist that much don't get their head on straight so to speak.
I assume the author left it open ended so that each reader can think of his/her own ending to the story, but when you know how a person acts when they behave like Malena did (for people with experience, or have friends like that (which I have one, and I fortunately persuaded another one so it didn't become two)), there's only one ending to that, and considering how her friends behaved, well, she doesn't have someone to help her.