loveI have a great love and respect for her.
adorationShe described her complete adoration of her brother.
romanceTheir relationship was nothing but romance and bliss.
passionThe passion had gone out of their relationship.
infatuationNo one expected their infatuation with each other to last.
crushinformalHe had a crush on his French tutor.
head over heels (in love)He fell head over heels in love with his best friend's sister.