One of the favourite bits of advice that I brought away from the Michael Hauge workshop...
There must be good reasons to bring your hero and heroine together at the end -- in other words, solid ways the romance character (love interest) relates to the hero’s arc. (Or heroine's arc)
Otherwise there’s no logical reason why they should be together – and there’s nothing worse than the character who more or less implies: `I love you because we’re in this movie or book together.’
It's not purely about attractiuon. Think about the ways your hero and heroine match up. Think about their goals and needs and wounds and how they compliment or heal each other. And yeah, wanting to be kissed in the rain is a very simplified example of a character's need or goal -- but the picture's nice, isn't it? :)