For those reviewers bashing the "Tessa and Hardin fight, have sex, and make up" on repeat -- that's their relationship. Despite the fact that they have a cool apartment (which doesn't belong to them), and have sort of jobs, they are college students. She's 19, he's about 21/22. They both come from broken homes.
Tessa's mother controlled every aspect of her life, and basically brought her up to believe that men could not be trusted. Hardin witnessed his mother being assaulted, and was subsequently abandoned by his father.
It's not as obvious in the movies as in the books, but they've only been together (on and off) for about 7 months by the time this movie is over. Tessa is still a freshman and Hardin is a junior. As the movies have progressed, you're almost fooled into believing they're growing up (due to costume choices and lifestyle), but that's far from the case.
They clearly do not communicate well, and behave very rashly. Hardin still self-medicates with alcohol, and probably has PTSD. He gets tagged as a 'bad boy' but that's not accurate. It's a persona he's adopted to isolate himself. Tessa exhibits her mother's controlling behavior and clearly has trust issues.
This line sums it all up "There is a big difference between not being able to live without someone and loving them.” Hardin and Tessa are co-dependent, and won't be able to be together until they stand on their own two feet.
This movie falls a bit flat because there's a ton of story that was left out. So it's just fight/have make up sex/repeat, which is a disservice to the story. Further, there really didn't need to be four books/movies. Three max would have done the trick. On screen, it's very repetitive.