She thinks she wants you back. Doesn’t mean she’s serious - but she’s seeing the consequences of her actions, including losing you and another woman being involved in her kids’ lives and it’s freaking her out.
It’s not unusual for the WAS to want us to be waiting on the shelf as their Plan B in case things don’t work out with the OP, and to suddenly get interested when the LBS moves on.
Question for you - would you be interested in reconciliation if you weren’t with new GF?