this is not a good sign, especially in the love of magic. Trembling of the flame means - your indecision, or you're shaky in his desire. (doubt it). in addition, it may mean - problems and conflicts.
but such "behavior" of the flame is not the worst thing that happened to you. bad is quite another .... ((((((
the wind could be doing it, yes, but if you're in a room with no wind/open window/fan then it's the spell. i posted a list of what each one means, and that's a bad sign. http://www.spellsofmagic.com/spells/life_spells/fortune_spells/10648/page.html