Is he allowed to stop me from taking them even though he initially said okay with it?

A couple months ago, I planned a vacation in Europe for the end of this year with my 2 teenage boys, 13 and 15. My ex was fine with it and came with me to get and sign for their passports. Several days ago, my ex got angry with me and he said out of spite he would no longer allow the kids to go to Europe with me. We are leaving in a month, I already have all of our plane and train tickets as well as our hotels and activities set for all the countries we will visit. I have copied documents showing his signature on the passport forms along with the time frame we would be gone and the countries we were going. I have all the texts showing that he said he was withholding the kids from going out of spite and not due to any concern for them. This trip has cost me thousands of dollars and most of it are non-refundable. We have joint custody with me being the primary parent, so the kids live with me and he has every other weekend and we split holidays. The child custody agreement does not indicate any traveling/vacation arrangement, only that I cannot move out of state with them.