S.
M.,
I am sad with you! My oldest daughter will be going to kindergarten next year, and I'm already kind of grieving that loss.
I think what you're feeling is so normal, and it would be more sad if you were not going to miss him. I don't have any great answers, except try to make the most of this time...find a way to talk to him and your husband and let them know how you feel, but that you're not focused on your feelings, just wanting to share how much you love him and have loved this special time of 18 years with him. This is a unique chance to express lots of love to your son, so go for it!
I would suggest coming up with ways to really celebrate everything, since it will never be the same for any of you after this. And it's possible he and Dad are feeling the same way, too. And the other kids may feel it but not know how to express it. I believe the more you just lean in to the feelings and find ways to hold on to each other and celebrate what you've had, what you have right now, and what's about to be - that will make it easier for everyone. Make him feel very loved and special, and plan special ceremonies for him. Especially since your husband is a pastor, I would say have a family ceremony of sitting him on a chair with all of you around him. Place your hands on his head or shoulders and each one say a special prayer for him as he goes into this new world. You can do this more than once! It gives everyone more opportunity to express their feelings and love to him, cover him in much needed prayer protection, and establishes a pattern you can use for other events in the family.
Also try to take a special trip this summer...maybe even just a short weekend away in San Antonio or Galveston. Something that can be fun and memorable. Even just going to Ft. Worth or nearby and staying in a hotel is usually enough for kids (if there is a swimming pool there!).
Bless you as your world changes...thank God for the gifts you have in these children and the opportunity this son has...work hard to keep your family's hearts turned towards each other.