why would she slap him tho (spoiler-y)
I don't get why she'd slap him on the bed in that hotel room...more than once. I guess it was just an error of judgement on her part. Thinking she was being playful but it set him off? But even when he clearly stopped being playful she did it again, yikes. I know someone who used to get beat upon as a child, and she would actually hit or hurt someone if they even touch her unexpectedly. As an instinctive reaction. So to me, in the movie, her hitting him didn't seem like a good idea. I mean when a dog growls you don't hit it again....
Anyway...I'm not victim blaming or trying to say that he was right. Dude clearly had emotional problems. He seemed to be trying hard not to be like his dad but sadly the abusive patterns were creeping in...with the put downs and controlling behavior starting. I could see how he was likable/charming too so ... the title character was actually pretty strong-willed at the end of the day. She stood up to him a lot and bailed before it got too out of hand, even after he was crying. So, good for her. I do think her slapping him the second time was part of that defiance too, even though I think it was a dangerous idea. She was just "testing" him (like trying to eat the pie earlier, too, even when he told her not to), because if he was someone who'd get all angry and controlling as easily as that, she wouldn't want to be with him.
...so I guess I answered my own question as to why she'd slap him even the second time. It just made me cringe and think she was very foolish tempting fate like that!