Is his stepkid’s education his responsibility? 

When couples get married, they often combine all of their finances. They don’t differentiate between his and her money: they make all their financial decisions as a team, which helps them build wealth better than they would if they kept everything separate. 

It’s easier to combine finances without issue when you are marrying for the first time to someone who doesn’t have kids. If you have kids and are marrying someone who also has kids, things can get a little fuzzy financially. A stepparent might not feel comfortable using their hard-earned cash to fund their stepchildren’s extravagant extracurricular activities. They might want to keep finances separate so their money is used only to support their kid, and vice versa. After all, if their partner is receiving child support from their child’s other parent, it might get murky if they have access to that money and use it to support the child’s stepsibling.