As someone exceptionally paranoid about bodily fluids I’d say your chances of getting anything are miniscule.
Firstly.. what was the guy like. Sure he’s a scumbag, but assuming he’s driving a white van he’s probably not a heroin injecting junkie with blood seaping from his gums.. As such in reality it’s no more likely you would get anything than if you had snogged a random in a bar
If he was the type of character who looked like he may be ‘riddled’then even still chances of infection would be minimal at best.. Theoretical but near impossible for hiv, and miniscule for hep b and c. If these deseased were easily spread through saliva then we’d all be screwed..
Forget about it and enjoy your Christmas.