If you have not yet, next time you see her flat out ASK HER if there is a problem. She may not even realize that her lack of "attention" is hurting you and your son and probably her kid(s) too. NRE makes us blind to many things, especially whether or not we are neglecting prior relations and commitments.
Talk to her about it. If she still doesn't register that there could be a problem, then move on and leave the bridge light on.
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.