Getting caught cheating is a hard slap in the face for anyone. You have to remember that you brought it on yourself, if you would had a condom on with your hookup this situation would not have happened. I’m sure you are well aware of this fact but it’s still good remembering it so you won’t do the same mistake in the future.
Getting a girlfriend back is a issue many of us who coach men get and it’s not a easy one. Your ex girlfriend wanted to have a monogamous relationship with you because she was in love with you. That means she have feelings for you and right now she is feeling hurt by you going behind her back and fucking other women.
If you want her back you should man the fuck up and tell her you did wrong straight up. Then not contact her until she is reaching out for you. If you are not clingy and accept the fact she may not contact you again there is a chance she will contact you again, then you will have a shot with her again. For now give her space and don’t contact her at all. Remember most girls are not angry you fucked someone else, they are angry you did it behind their back.
Just some piece of advice