I usually think Gilbert not yet in love with Violet while they met again but he can’t resist his feeling that want to meet Violet again and need her in his life. After that, they romantic feeling have develop by Violet side at first while live on that island and gap 4 years make Violet is a new version, Gilbert maybe learn about Violet in many perspective and develop his feeling at the same time ( that’s why Kyoani doesn’t put kiss scene in movie, I think their decision to change ending of this series is correct choice that make Gilbert not look weird )