Talking to a therapist to learn more about you, about what it is within you that desires the attachment to your co-worker. This comes from within and it is about something you desire, openly or secretly.

Some thoughts:
Can you identify more about the thought(s) you are having when she 'pops' into your head?

What does 'lost in the clouds' mean? Dreamy fantasy? About?

Who do you see? A therapist who does depth work, such as a psychodynamic psychotherapist. There are other types that others can recommend from their experiences. The important thing is to have someone to talk to about this before it becomes a work or marriage issue.