Capital gains / divorce settlement

  • Hi - I have a question about capital gains. My divorce was finalized in 2019 with the MSA agreement stating that the the net proceeds from the sale of the home will be divided 50/50. My ex husband is the only name on the title . His accountant is telling him that he can only use a single owner exemption of $250,000 on the capital gains. My question is why can we not use his $250000 and my $250000? The sale was part of our divorce settlement. We had a defined date of sale. He could not sell the house until our kids were 18. Putting us at a sale of august 2023. He now wants me to pay half of his tax liability. Thoughts?