Maybe it's just an ordinary meal for you, and it doesn't matter if you take him, but we will take our friends to dinner on some occasion. Your classmate's wedding, she invited you and your family, or your other half, and it would be strange for you to bring a girl who is not your other half.
If this girl is sensible enough, she won't agree to attend your classmate's wedding with you unless you want him to play your other half. Weddings are all banquets for their relatives and friends. As a saying goes, guests don't entertain guests. In other words, if you are another guest, you can't bring another guest. It's a matter of courtesy.
In short, such behavior is inappropriate, try not to do such a thing!