Just ask her.
act as if you didnt know about this and then ask them for the story.
...what?
Nope, his ex-girlfriend Hanna Warnes cheated on him.
When a couple breaks up then 'ex' means you are no longer a couple and she probably has moved on (as you should) or, she is embarrassed about the whole mess. Expecting to be friends with a girlfriend that cheated on is jumping from the frying pan into the fire ... in other words, move on and don't worry so much about your ex girlfriend not talking to you.
If it was your ex then he hasn't cheated on you because he is your ex. He cannot dump you because he, or you, have already broken up. What you should do is try to grow up.
ask them
If your 'ex' dumped you for an 'ex' that dumped her, chances are she's gonna get dumped again.
Sex
She obviously doesnt love only you if she cheated on you with her Ex. I;d stop seeing her immediatly, I mean she did cheat on you!
Don't go back to your ex. She is your EX for a reason, & hello, she cheated. Don't hurt someone else because you want to be reckless. If you have feelings for both women, just break up with your long distance girlfriend, but don't get with your ex. It's not fair to string your current girlfriend along or lead her on because you don't know what to do with your life.
ask her
Ask her out.