I agree with many of the others that have posted so far.

I hear that you say you are losing your son, but that is only one way of looking at it. My in-laws feel that way and it's been extremely hurtful to both me and my husband. Instead of looking at it as losing them, maybe try to see it as gaining a new potential daughter. Change is hard but it doesn't have to be bad. Your son wants to include you, which is why he invited you. Our children are only little for a certain amount of time, and then they branch away- not due to lack of loving or caring for us, but because they are growing into their own lives.

Anyway, I am coming from a caring place- I'm only on the other side of this equation. I hope it gets easier for you.