Is this really me?

I just finished balling while cleaning the dirty dishes. No, the act of scrubbing meatloaf off of a pan didn't make me weep, it is the realization that I failed my son today. I never thought for a minute that I would be perfect, but I never thought that I would stand by and let the pains of my youth harm him. Here is the story:
I have a step daughter (SD), this relationship is rocky to say the least. I also have a mother in law (MIL), and that relationship isn't much better. I can say that I have tried to be peaceful. That I have tried to look past the looney toon ex, the lies from a child, and the foolishness of my MIL, but I think a time has come when I can't. My MIL has made it clear on many occasions that my SD is her favorite grand child. I am not over exaggerating. She has actually listed the order in which she likes her grand children with SD being number one and Baby Boy NOT EVEN BEING MENTIONED!!
I was not the favorite grandchild. My older brother was loved, my oldest brother the least liked, and that left apathy for me. This caused many problems. I resented my older brother, and I held anger toward all adults in the situation for not behaving better. This truly hurt me for many years, and to be honest still does. I always wondered why I wasn't good enough. What made me worse. No matter what I did it never made them happy. In some ways I was also jealous of my oldest brother, he may have been hated, but because I was a girl I was invincible.
I have spoken of this because it is now happening to my son. My MIL brought my SD on a shopping spree under the guise of bringing her along to help her shop for Christmas gifts. My MIL dropped at least $200 on my SD. She bought her a lot of clothes because me SD lives with a moon bat of a mother who can't be bothered to spend her child support on the child. She has to pay for the lives of the two people she is fucking. No that is not a type-o I really meant two. She is a whore, whose vagina has been seen by more people then Brittany Spears. Yes, I am including the no underwear getting out of the car photo viewed by millions. Yet I regress. So my MIL takes the SD on this grotesque shopping trip and what does she get baby boy?? Some dollar teething rings from the grocery store as an after thought because she FORGOT him until Crow mentioned him.
But that is not the worst part. The worst part is I saw this and said nothing. God help me I just sat there while my son, my only son, was treated like a second class citizen. I feel like such a bad mother, I said nothing. I became the person I actually despised. I sat there and let him be treated like he wasn't good enough. And for what some babysitting when I go to school.
So now you know why I cried. My silence will haunt me.