To be fair I think Callum does like Shauna, and liked her more than all the other original girls, I think he just doesn't like her as much as she likes him. There is like and there is like, and I think he liked her enough to go along with it, but not enough to knock back someone he really fancies.which would be molly.
I think we are all reacting to shaunas feelings, because we all feel bad for her, but in reality, we all know, he liked her but wasn't feeling it as she was.