If there is not much contact in the future, you can not go. Reason: I have something to do on the wedding day. Of course he knows you don't want to go.
If you want to be friends in the future, you must go.
second
You are a man, and so are your colleagues. You'd better go. Colleagues are women, so you can't go.
If you are a woman and your colleague is a man, you don't have to go. Colleagues are all women. Let's go.
third
Generally, marriage is a dinner party, so you have to find some reasons.
1. Business trip-people are not local.
2. Working overtime that year (a bit far-fetched)
I don't understand.
fourth
If your former colleague calls you to prove that he cares about you and treats you as a friend, you must go.
Just don't call!
fifth
I promised to get married before. If it were me, I would go back even if the sky fell.