NTA. This is the main reason why me and my partner talked about having shared expenses in the future. We will both have separate accounts and one shared to pay bills. Since your wife is a SAHM you can open another account for her and give her a monthly “allowance” of some sort. I know it sounds bad, but since she has no respect for you and your son in terms of finances then that’s what you’ll have to do. It’s obvious she’s trying to make a point that her bio son is more important to her than your son. What I’m so shocked about it is the fact that she’s not making any money and didn’t contribute to the 8K, yet feels entitled to spend it as she sees fit. A serious conversation needs to be made and from there see if this relationship is worth saving.