It depends with the person and the reason why we broke up. Some ex are good and you might find out that you're the reason why you broke up or maybe a slight mistake made you guys to break up. You'll start having feelings on your ex when you meet someone new and when you compare the two you find that your is better than him/her.
For me, I do have feelings for my although it only lasts like one day then I forget about him again. Most a times am always tempted to text him and tell him how much I miss him but then I come back to my senses when I imagine how I will be stooping low. I read a certain book, it said that when you break up with your ex never call/text him because they'll think that you want them back. If I move on and the man doesn't seem to be what I expected of him, I usually quit stay single for sometime before finding the right person but going back to my ex, I will never.