Most Helpful Girl
Would you trust her again not to cheat? I ask just because trust is important and you deserve that if you're going to enter a relationship with someone who has previously done this to you.
I would maybe start a convo in a casual way to see how she's been and what's new blah blah. And casually ask later in the convo about the other guy, and see!
Have you not talked to her since the break up?