After the engagement ring, you need a wedding ring. After all, you need to get married, not just engaged! If you can afford a diamond wedding band at the same time, that's great. But I have worked with many customers who have budgetary constraints and a plain wedding band has to do for the wedding itself. The diamond wedding band just has to wait.
When the time comes for that next piece of jewelry, a diamond wedding band should be next. It doesn't have to match exactly with the engagement ring and it doesn't have to fit flush with the engagement ring either. It can be worn on the opposite hand from the engagement ring. Fine jewelry complements other pieces, they don't have to match exactly.

