You can hardly read the news anymore without reading about a music celebrity cheating on or being cheated on. Ari's past boyfriend, Ari herself, Rita on Calvin, the long-discussed Jay-Z and Bey rumors, etc. Wtf is with these musicians and their significant others? They need to keep it in their pants...

Did Ariana actually cheat on him?
I'm so confused

It's because they're always on the road away from their SO
Touring and promoting and meeting new people

I think it's fairly common with normal people too, but less publicized and it's easier to keep it secret if you're not famous.