How did Gerald Croft contribute to Eva's death?Watch
It's implied that Gerald did love Eva however, due to him being her social superior he disposed of her when it suited him, abusing his social superiority and demonstratinf perfectly how priestly thought the upper classes to be ignorant, manipulating and abusive of the lower classes
but nevertheless he did use her when it suited him and that is more the exploitation in my opinion and unfair treatment of the lower class that is never justified
Gerald had the perfect opportunity to help her and may have had good intentions at first, but like Mr Birling and Eric he thought that a problem could be made to go away by throwing money at it.
I think Gerald was included to provide more of a range of characters. The Birlings all have features that make them appear as stereotypical villains. Gerald offers a slightly more sympathetic character, perhaps to add a small sense of balance.
That seems like a hard question and hopefully AQA are nice enough to give you something better.