In my state, you have to prove that money is separate property, which typically means it was not commingled at some point during the marriage. The burden of proof is on him. He was planning to buy something fun for the two of you. The account is in your name.
I wish I could argue I had a bunch of money set aside for a future with my STBXW but since things didn't work out, I'm just going to take it along with me since it's mine lol.