My boyfriend took "What happens in Vegas, stays in Vegas" way too literally. 

THE UNDISPUTED CHAMPION OF EDITS : ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HXaqZV_CzBE.html (AITA for not letting my husband meet our first-born child?)

"He's literally studying to be a clinical psychologist," for all the wrong reasons, I'd bet.

"What happens in Vegas, stays in Vegas" was a promotion for adult freedom and was said by R&R partners, and since has been taken as an excuse to do whatever you want

Yeahhh I could tell where this was going the second he refused to stay with her. Long-term partners are more important than Vegas thrills, and choosing to make that sacrifice or not is something that will stick with them forever.

I you have to set all those boundaries, why would you even call it a relationship?

Hm… if I’m serious about my gf then I’m probably skipping this vacation and staying w her. The brownie points will be worth it

Her wischi-waschi bs at the beginning was just painful 🤦 and even when she wasn't sleeping with him she still slept next to him ugh

Op should act like she agrees with what happens in vegas stays in vegas then go to vages and do the same and tell him. Let's see his face then

Avoid even the appearance of evil... Don't even bring the girl back to your place if you don't want to break up... Also my dude took the Vegas tagline to encourage people to blow money as an actually accepted thing...

I will say that you are part of the problem, thinking that the saying has any merrit. There are a lot of ways to put this, but you're giving all sorts of infidelity an inch, then wondering why people take a mile. Fact is that what happens anywhere follows you everywhere, and that's where you should draw the line.