What was the reason for breaking up? It seems like it was not legitimate to break up over a stupid text, it was a misunderstanding that caused all bottled emotions to run out. She stares at you because of the change that has occurred over the 3 years and definitely has thought about you from time to time even if she has been with another guy. I'd assume you have thought of her a few times randomly? Have you tried talking to her or even serving her from food? See how it goes, don't be afraid or let emotion get the better of you, if she snobs you when your being nice then pull her aside and talk to her in private. Sometimes to find the answer you must face the problems you do not want to, that way you can get past and move forward without hesitation.
What you want sometimes may be your brain only seeking the comfort and satisfaction. But what you really want to do with your gut feeling, instinct and heart is reality.