Most Helpful Guy
You broke her heart and that takes time to heal. you also need to think deeply if you really want her back or just don't like not having her.
IT's also worth noting that you are still with this new girl. If you really want to try and get your ex back. End it with her, take some time (weeks) without any of them and focus on yourself. Then if you still want to have your ex back go and talk to her and ask for time to prove it.
Trust is a hard thing to build and even harder the second time. You need to not be with the new girlfriend while trying to do that for starters.