The problem is ceejayjay,that it is difficult to separate howwe feel in ourselves, from how we respond to the events in our lives. I ama glass full andbrimming over person married to someone whose glass tends to be more than half empty and I can see how different our reactions are to the same events, good and bad.
I would just tell your son that you would love to see himm and his girlfriend over Christmas,when would they like to come and go with their response,then forget about it until a week before the event. Do not under any circumstances,try to compete with anyone elses Christmas. It will feel false and unreal. Just be yourself, act asyou always do. When our children visit they unconsciencly want the familiar. To come home and instantly know where they are and who you are. If yiur son and his girlfriend are as nice as they sound. They want to see you as you are.