What does it mean that my boyfriend doesn't want to attend my colleague's wedding banquet with me?

If it were me, I wouldn't go either. First, because the other party only invites you to a colleague's wedding banquet, and that colleague is not your good friend, unlike a good friend, you can bring any friend. Second, men are proud. It's inappropriate for you to suddenly take someone to a colleague's wedding reception. I don't think he meant anything else, so you should respect him in terms of manners.