If you think about it shaugna is literally this years amy. She's really not behaving that much differently.
The only minor differences are she has not dropped the L word, but did say she'd quit her job and move from London to Manchester to be with him. She also had enough awareness to know he might dump her. But clearly deep down thought he wouldn't.
To be honest, I'm not really sure what Callum has done wrong, he is on a game show. He did like her, just not that much. He clearly prefered her to the other girls so coupled up.
He didn't however lead her on past that, he didn't show her affection, would even go to sleep without saying good night to her, there was no fooling around, cuddling, smooching, etc. I'm not even sure they actually did "do bits" like she said. If they did it was very minor.
Other than be in a couple with her, he did nothing to warrant shaugnas thought process that this was the real deal and he'd want to live with her and be in it for the long term.
It really is very similar to Amy's behaviour last year with Curtis. I think because shaugna is fundamentally more likeable than Amy people are excusing the behaviour more than we should.