So sorry,
When I read your letter, it was like I received it myself!!! How familiar...It boggles my mind that a woman can do this to her children...Bio mom, in our case, uses her three kids as meal tickets...guaranteed money every month...It's sad and really, only the kids suffer...but, keep the faith and know that eventually, step son will realize what kind of person she is...It might not be for a while, but it will happen and he will know what you and his father did for him....
Bio Mom accused me of being sexually assaulted as a child and told my SO that I was NOT to bathe her children as a result...Can you imagine??? It is so untrue and I don't know where she gets off...Of course, I don't listen and I bathe the kids everytime they visit...She's a lunatic...and my SO knows it and supports me 100%...
Good luck and I hope your holidays are wonderful...