My son is graduating, my husband and I are no longer together. I asked him if he could contribute to the dinner after the ceremony he said he could not. My response was since I am paying an it is a small intimate affair with close family and friends, his girlfriend should not go. Was this the "proper" thing to do? What is protocol for something like this?
This can be a sticky situation in any family and not just because of divorce. Sometimes, we just want to exclude a family member we think may be disruptive; one who drinks too much for example.
You mention that your ex-husband did not contribute, however, I doubt this is about the cost of the meal, is it? Then whether or not the grad's dad helped pay for the meal is not relevant to the real issue here.
This brings us to the real question. Would you rather upset your ex more than you celebrate your son? My advice is to ask yourself, "For whom am I giving this dinner party and what would the guest of honor want me to do".
Unless it will upset your son to be involved in the decision, ask him how he feels about including his father's girlfriend at the dinner. And then the two of you decide together. It is always proper etiquette to put our personal feelings aside and look for a solution that will bring harmony and good will to the occasion.
If you have already excluded her, perhaps this little discussion will be helpful for the next family gathering.