Put it at the end of a montage, after the photos have done the storytelling, so the message becomes the closing beat. Pair it with a gentle romantic clip beforehand to set the scene, then let this clip deliver the line on its own.
About this sound
This six-second clip is a warm voice saying 'I love you baby' in a soft, unhurried tone, with a gentle lift on the final word. It feels tender and sincere, like a quiet message meant for one person, and it can make a listener smile or feel suddenly shy. It works best when the moment is already affectionate and needs nothing more than those four words.