Yes, you have to RSVP. Yes, you have stick to it. And do it in a timely fashion. The happy couple has a lot to plan during this time, and they need an accurate count of the guests. Each guest costs them a lot, so overbooking is rude and really hurts them. If you wait too long they may not be able to add new guests, or it may cost more. They care about you enough to invite you to their wedding, so give them the respect they deserve and RSVP.
