Neither Bulma nor Vegeta referred to each other as married in the Boo Arc. I can't remember if they ever did so in Super. If not, they likely remained unmarried. If so, then it would be between Boo's defeat and the start of Super.
Was it just dinner though? Either way, they're just unofficial couple so it doesn't matter to Vegeta whether they're married or not but Bulma is his wife according to him. you you1