Gerald is not a member of the Birling family and his family - his mother isLadyCroft - belong to the aristocracy while the Birlings do not. Gerald's money, unlike the Birlings, is not based on the harsh treatment of factory workers like Eva Smith. Therefore Priestley presents him in a more sympathetic light than Mr and Mrs Birling. However, he is older than Sheila and Eric and less susceptible to the Inspector's message so he doesn't develop as much as they do.
Gerald knew Eva better than any of the others and certainly treated her better. His grief at her fate is genuine and personal: he nearly breaks down as he remembers Eva and he says, 'I'm rather more - upset - by this business than I probably appear to be'. In more modern times he might not have kept such a check on his emotions.
He's not entirely blameless: Eva is heartbroken when their affair ends; Sheila is understandably hurt and he has not respected the commitment he made to her. But the final judgement is the Inspector's who considers that Gerald 'at least had some affection for ..(Eva).. and made her happy for a time'. This cannot be said of the others; Gerald treated her as a human being.
However, at the end of the play we see that Gerald has not learnt from his experience with the Inspector, as Sheila and Eric have. Having uncovered that Goole is not a real inspector he is too quick to tell Sheila that 'Everything is all right now' and ask her to take back the ring. The fact of his infidelity should have told him to give Sheila more time; we get the sense he hasn't fundamentally changed, and any guilt he felt about his treatment of Sheila is short lived.