She knows.... she's reading here.
She knows its being said he lurks on hot stuff insta.
Thats why she's trying to prove he's into her.
She knows we think she's abusive towards him.
Thats why she's trying to show him being hateful towards her.
On a serious note nobody has to stay in a relationship like this, it won't change. As you can see Demi is always one step a head. If you're in a relationship like this the other party will go out of their way to make you look like the bad guy.
There is help. I'm laughing at the two of them, but there is a serious side to this, she's chipping away at him and he's reactivate. Thats where it becomes a bit of a grey area, but I see it, Sean would need a lot of support to leave her, if he made that choice he'd probably be happier.