To me, the song seems to be about a relationship (or lack thereof) with someone who is acting as if he is interested in the singer but who ultimately won't commit to her in the end. If she gives him "sugar" - which can be interpreted as love, sex, or both - he might give her "something elusive and temporary" - the promise of a relationship that's never actually going to happen. She's already seeing the signs that he can't follow through and knows that she should just leave him alone, yet she still wonders what would really happen if she got involved with him anyway.
To me, the song seems to be about a relationship (or lack thereof) with someone who is acting as if he is interested in the singer but who ultimately won't commit to her in the end. If she gives him "sugar" - which can be interpreted as love, sex, or both - he might give her "something elusive and temporary" - the promise of a relationship that's never actually going to happen. She's already seeing the signs that he can't follow through and knows that she should just leave him alone, yet she still wonders what would really happen if she got involved with him anyway.