Firstly, i completely understand what you are saying. The fear of being let down often makes us refuse help, especially for ACoA's.
I know this is a bit of topic for the thread, but do you maybe like this guy? Because the way that he is acting implies that he may like you. If you dont like him, then keeping it professional is the best way to go. But if you do like him, insisting on paying him might push him away. But making food is always a good neutral payment and a nice way of saying thank you, whether you like him or not.