I said this yesterday, I think he is having a hard time that she is more famous and successful than he is.  He used to be the IT guy in the industry, and now, not so much.  He hasn't had a hit song in a long time, whereas she obviously has.

Here's what an insider said

"She's stressed about the tour, they've been fighting. It is probably for the best, because she is going to be on tour for forever. Of course this happens all the time, I can't keep track anymore. But for now they are done."

Hopefully they work it out, I always thought they were a cute couple.