I don't think your son telling his dad that having the OW there would only cause drama between you and dad would be, in any way, beneficial for him to hear.
I don't think that that puts you in a good light at all...
why would there need to be drama?
the best thing would be to be able to be gracious for your son's sake. It is his day...his graduation...and he shouldn't have to worry about drama between his parents
