You would not be selfish to go without your son. My husband and I have 4 kids 23, 20, 17, and 14. None of them would be able to pay for their own trip. That means that we would need to pay for 6 for food, accomodations, airlines, entertainment.... We would never had been able to have our dream wedding if we took our children. Plan a small getaway for the three of you before you leave and explain that you are doing that with him instead of taking him to the wedding. The wedding/honeymoon should be your special time with your husband. Kids actually accept things better than what we give them credit for. I was 16 when my mom remarried and I wasn't invited and didn't scar me for life