Slowly, don't ASSume that he treated her more courteously... just don't go there. Stay in the moment, eat if you want, don't eat. Focus on the good stuff. When H does extend you a courtesy affirm, affirm, affirm.
Don't allow yourself to sabotage an evening out. Don't give OW the power to bother you.
You are doing so well!
Relax. Appreciate. Be calm. Laugh. Enjoy. Be secure. Be loving. Be loved. Don't personalize. Don't ASSume. Accept. Be grateful.