Advice..

We finally told my step son he is having a baby sister and he clearly told us that he already has a sister with his mom and he is not having anymore. It hurts me due to because my partner feelings got hurt . My husband tells me he wish he would be happy for him. We've been together for 7 years and living together for one year. My step son is a 9 year old going on 10 spoil brat and throws fits every time he is told to do something or been told NO. Yesterday he got close to me and did a punching phrase close to my belly , I am worry that he will never accept her ... and break our family apart