I can't remember the university, but there was a study done about how long allergens transfer via saliva after eating. It was determined that someone kissing a person who ate something the other person is allergic to can remain in saliva for over 4 hours after eating, flossing and brushing teeth. So gluten may be transferring to you when you kiss your girlfriend. Is it practical to ask somone not to eat for 5 hours before seeing you? Don't know.