They are both still hungover. And saying it would happen in high school and not college, well they have been out of high school alll of one summer and a few weeks, they are bound to still have some immature ways.
And being super affectionate and dramatic the day after a party is normal. You drink to much, you make out, next morning you're like OMG that was so funny love you! A few coffees and long shower later you're thinking, shit.