It was a serial posting a couple years ago. Male was graduating hs and his parents took him to disneyworld (although never mentioned by name). At the last minute the female cousins and their parents invited themselves along which pissed him off because he always had to share his "stuff" with them and they were spoiled. He hooks up with a girl at the hotel pool, then later the oldest cousin. Then she crawls into his bed and he gets her off before realizing it's the middle cousin. Then there's yet another girl staying at the hotel, and it comes to light that his parents and his cousin's parents swap or play together. They only have a few more days left in the trip... and either I missed the ending or it never finished. It's been bugging me this whole time they I never found out how it ended.
