If it were me...I would make the decision for him. He is obviously keeping you as a back up in case things fall apart with this younger woman. Don't wait for him to decide to choose you...you should choose YOU.
The co-parenting stuff will work itself out in time...But you need to be the positive roll model for your children right now by having self respect.
Please please be kind and generous to yourself Pandalover, and welcome to P.C