The female was a mean person (and a poor character)
I just watched the movie and had to create an account because I was shocked about the female character and had to hear your thoughts about it.
My main problem is this : why does she cheat on Matt Damon with Leo Di Caprio ? We had no clue whatsoever that she was unhappy with him, she even said to Leo that her love affair was "very serious". And even if she was unhappy, then why not leave Matt Damon first, like a decent person ?
In her situation, the only thing she could have done when Di Caprio tried to kiss her was : get offended… But she didn’t and slept with him instead, which was out of tune with her character and everything it represented (a nice, caring, honest woman).
Not only does she cheat on him while moving in his place, but she has not the slightest remorse while announcing her pregnancy to Matt Damon even though she knows it may not be his baby.
I don’t undurstand why such a vicious and evil behaviour was given to such a calm and peaceful character. It was so out of place.
It would have been logical if it was a mean of saying "There are no good people, even among women". But that’s not what Scorsese wanted, because we can feel all along he wants us to side with her. Therefore, I think it’s a mistake of writing because it fits nowhere.