Totally predictable tactic by women after realising that the grass is NOT greener on the other side.
Now, Bob, for the sake of your present relationship (if you value it that is), cut the ex. off as completely as possible. Tell her that you are no longer interested and that she (the ex) is history.
People will despair of your attitude if you so take me advice, but if you don't, then you might find that two relationships are bu99ered up.
Also..the kids.....they are mentally stronger than people give the credit for and anyway if anything turns out untoward for them, you will get the blame.
Sink the EX.............now.