Aspects. There are other drivers that you can use, but Aspects are how the important plot points of the Dresden Files are kept in play mechanically.
Characters also have a set of traits called aspects. Aspects cover a
wide range of elements and should collectively paint a picture of who
the character is, what he’s connected to, and what’s important to him
(in contrast to the “what he can do” of skills). Aspects can be
relationships, beliefs, catchphrases, descriptors, items, or pretty
much anything else that paints a picture of the character.
If the character is connected to his fiancee, and wants to reconnect to her, represent that as an aspect. The player can invoke that connection/aspect to give himself more drive when he needs it, and you can compel that connection/aspect to give him an imperative to do things that move him towards this goal and tie him to this connection.