Didn't Styles decribe her as "asexual"? I thought one of the stories for the break up was that she wasn't in to doing much physically with him, which is obviously something no horny teenage boy is going to put up with for long!
Of course, if rumour be true, 'tis little wonder that she wasn't (allegedly) very interested in a physical relationship.
Would you have sex with him? He's probably got all sorts of STDs. I can't say I'd blame her for not wanting to have sex with him.
If that's the case, good on her for not giving in to keep them.