[Link for the term "Whipped" I'm using.] TL;DR at the bottom.

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So my best friend, let's call him Sam (18m) and his girlfriend, who we'll call Ashley (17m) have been dating for over a year and a half now. It's clear as day that no one likes Ashley. She is very rude, to not only Sam, but to me, our other friends we all hang out with, and just everyone around her. She is a total bitch IMO. 

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Where Sam goes, she's there. When we decide to have a "Guys" night, she tags along. When she does, she's nothing but selfish, rude and talking constant shit while always touching and totally showing PDA. The PDA is the worst part. Sam is always paying for her food, meals, giving her rides to school then work. For context, Sam isn't the most...Fortunate man in the world. He's not poor, but nowhere near rich. He's about almost at low class citizen area. SHE comes from a very rich family. Has a million dollar house, lives in the best city, has cars from a Tesla Model X, to a Mercedes S-Class. 

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Like I said, he's totally submissive to her and does whatever she wants. Sam is giving it his all for Ashley and she is literally just saying, "Meh. Pay for my food." Sam is currently balancing 2 jobs and high school while Ashley doesn't even have one. The relationship is totally lopsided and it's clear as day that Sam is whipped. There was a time where Ashley slept in the same bed as one of her cousin's friends at her house. And she claimed nothing happened. And of course, Sam believed her and laughed it off. He's even bought her a $200 necklace she has never worn before. Which was about 2 paychecks for him. She bought him a hat. He wears the shit out of it.

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She didn't even tell her parents until there 1 year anniversary, which was sketchy as hell in my opinion. He will go out literally every weekend to her house at 1am to go spend the night at her house to avoid her parents. Keep in mind they live about 30 minutes away. And he is always going over to her house. She's been to his house once and that was a few months ago. Sam moved about a month later and she hasn't even seen it yet. She is a terrible girlfriend and it's clear as day she is whipped, so WIBTA if I tell him he's whipped? Providing all the information and proof that says so. Or should I just keep my mouth shut and let him find out the hard way.

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TL;DR, Best friend is clearly whipped due to the influx of things he does for his girl, pays for every meal, drives out to her house every weekend which is a 30 min drive away, buys her expensive jewelry, she's a freeloader and yet she's extremely rich. He is pretty low class. She has been suspected of even cheating (which she probably has.) Our whole group hates her and thinks the same of her. Should I tell him he's whipped or just let him find out the hard way?