The first part of the scene: Aerith has been captured and Ramiel's in a stand off. After a bit he's left with a choice, let her drown or get him. He jumped in after her to save her, brought her to a near by beach to resuscitate her. He was successful and in that moment they shared their first kiss then shared their first passionate moment there. They've been inseparable since then.

Ramiel and Aerith belong to me
Inteleon belongs to gamefreak