Although the idea is tempting, I would urge you to proceed with caution. I have heard story after story about students who have been hurt in this type of situation. In almost every case, the student, not the professor, winds up devastated. The main reason for this is the power differential. No matter how hard you try, relationships where one person has more power than the other are difficult to maintain.
Professors have the potential to affect student's grades, reputation, and even career.
Even though you are no longer in the class, the fact remains that your professor was in a position of power when you met. This dynamic sets up the foundation of your relationship and is hard to change. On our campus, a written policy that strongly discourages consensual relationships has been proposed by the Affirmative Action office. I would also encourage you to think about why you are attracted to your professor. It is very easy to be attracted to people that we perceive to be in powerful positions.