I agree with what has already been said. As long as those romantic feelings are completely gone, I don't see why you shouldn't pursue a friendship. Then again, you said you had a fiancee, right? If you love her that much that you're willing to spend the rest of your life with her, then there really shouldn't be an issue because she's the one you want, even if some old feelings for your ex pop up unexpectedly. I mean, I believe things happen for a reason. You and your ex broke up because you were meant to be with your fiancee?
Nothing wrong with getting reacquainted and making a new friend. Friends are life's gift as an apology for family. XD
Always remember if you start to feel things heating up between you and your ex, run. Run before you end up on Maury. Don't question it, just run.
That's my two cents....
I'm dead ass serious, run and get the hell outta dodge.