YES - that is a quirk in how the stimulus laws were passed.
The PAYMENTS were based on 2018 / 2019 tax returns - those were the IRS's best guesses of what everyone was eligible for,
But the 2020 tax return (your filing status, the dependents you list and your income) is where the IRS determines what you are ACTUALLY eligible for,
They take that actual, subtract the payments, and they owe you the difference. if the difference is negative (which is what is going to occur with your ex), you don't have to pay it back.
So divorced / separated / unmarried parents that trade off who claims a child each year end up EACH getting the benefit for that child. It's the way the law works; Congress knew it and chose not to close the quirk with the 2nd stimulus payment.
