Step child issues

My husband has a 7 year old son from a previous relationship. This boy is very much in love with his mom, his mom can do no wrong and is perfect. Regardless of how much I try to love him and raise him right he does not recognize me as much as he recognizes his moms efforts. The boy lives with us and I do everything for him. While I had a job I bought him toys, food, and lots of books everything. 

In our culture (Zulu) if you impregnate ba woman and you are not married you have to pay damages and a "fee" for the child to be called by the fathers surname. We were preparing for our wedding and my husband couldn't afford to do everything. When we first met I had told him that before I take his surname I would like for his son to have his surname before me. And so because I believe I that I gave him the money and he went and did everything for his son, paid damages and the dowry for the changing of the surname. 

Since I now live with the boy full time he is disconnecting. Especially during the times where he hasn't visited his mom for extended periods, it's as if it's wrong for him to love me. Even at night when he kisses us to go to sleep he is eager to kiss his dad good night, and tells him that he loves him. He is not eager to kiss me and does not tell me that he loves me, even when I tell him that I do and ask if he does. He does however say when his dad asks if he loves me.

Anyway on my part, I am a strict parent, and since my arrival I have implemented a lot of changes, at age 6 he couldn't go to the loo alone, he had to call someone to wipe his bum after he did no 2, which I did away with, he was being given a bath at age 6, I stopped that, he didn't wash his undies, and he slept at whatever time even 10pm and watched everything and anything on TV. All things which have since stopped. His dad appreciates that and is proud of all those changes and is very on board with raising the boy to be self sufficient. 

He is now in grade 2 and can do a lot for himself. I have even created a routine chart for him that he sticks to on school days, with morning routine and after school routine, I did this so he can get into a routine and also so that I don't have to hover around him tellin him what to do all the time. 

I am trying really to mother here, which is something I have no experience in and no clue about. At times I feel persecuted by my husband when I do make mistakes. It's as though I am not allowed mistakes as a step parent. 

The bio mother is very rude at times towards us, she does not ask nicely for us to bring the boy, but he demands that my husband being the boy. She uses the boy to get to my husband and "control" him. I was very nice to her and have since booked her number because I will not stand for being disrespected or for her disrespecting my husband. She has now demanded that the boy come live with her( this is a story for another day way too complex, but she is engaged and her fiancé hates the boy coz he was a break baby) a part of me just doesn't want to live with the boy anymore, I too am just feeling myself just give up and disconnect, but my husband wants the boy to live with us, and so for that reason only I try for him. 

I just feel like a traitor deep inside because deep down I am tired and just can't deal anymore. The boy disregards me so much that he doesn't want me to get pregnant, when his dad jokes that he mustn't squeeze my belly coz there might be a child he punches it and squeeze harder. He even says that if I have a child it will be his cousin not his brother or sister, his brother is the one his mom gave birth to. I understand that he is a bit young to understand everything right now, but these things get to me and just make me want to take him to his mom and just forget about him, atleast for a while. 

I don't know what advise I'm looking for really, I just am tired of keeping all this inside to myself. I am tired of trying to love him like my own child when even I don't know what that is yet.