my SO constantly accuses me of favoring my child and it drives me crazy. I have a 3 year old son, and he has an 8 year old girl and a 4 year old girl. I treat his children like they are my own. I have taken them on trips, I have paid for birthdays, I have layed in bed with those girls on nights they were sick. I wake them up get them dressed, take them to school, pick them up. Cook dinner. I'm a full time business owner as well.  
He gets overly defensive of them when they have done something wrong.
The thing is, I have these girls more than I have my own son. We have them full time (because their mother became unstable and homeless) and I have my son every other week. I made sure we had beds for them, cloths, shoes, school supplies, and I enrolled them into school.  I do all of it because I love them and don't see them as step kids. I see them as my own.
I'm just at my end after today. 
All of the kids were being bad today, jumping off of furniture, screaming, running in the house, and hitting eachother. I kept telling them that if they couldn't behave they would all have to take a nap. They had time out several times. So finally I made them all take a nap after standing in the corner. My son never cried or fussed. He laid down and took a nap. The girls on the other hand screamed for 2 hours and wouldn't lie down. So when my son woke up,I asked my So, and I let him go across the street to his grandmothers because the girls were still in trouble. As soon as I was getting ready to walk him over. My SO starts in on how he gets special treatment and how I'm rewarding bad behavior. 
From my point of view, my son did what he was told, and his punishment was over. 
I'm just at a loss and don't know weather I'm in the right or wrong.