Well to me it's just love. I mean if I French kiss a girl in the street I don't get turned on but if it was my girlfiend then I would and I think it's because of love and well it's warm and she tastes good ;)
Guys love it when you tease them, then you start kissing them passionately. Like some guys have certain spots where they like to be kissed, such as the neck, and the ears. Try a variety of things if your relationship with him is deep enough.