Husband wants to adopt and you dont

What do you do when your husband wants to adopt a foster child in your care and you don’t? That is the current situation we have going on and it is creating a divide between us. My husband doesn’t understand why I don’t want to adopt our foster son but we have three other kids we adopted and all the work usually falls on me. I currently have two kids with special needs (three including the foster child) and I’m burnt out. He says if we don’t adopt him it’s all my fault and essentially our marriage is over. I feel he is putting the child before me and have told him it’s unacceptable.