If it's like the usual stories about why J-Ent couples break up, it's either one of them was caught cheating on the other, or it's a "they just started to drift apart due to their busy work schedules, which then lead them both to realize that it would be for the best to break up/just be friends" sort of thing.
[JFC MOD EDIT] WHILE WE KNOW THAT YOU WERE JUST TRYING TO BE NICE AND CONTRIBUTE, DDL LINKS ARE NOT ALLOWED IN THE MAIN PART OF HJU. YOU HAVE TO PUT THEM IN OUR SEPARATED "MEDIA MATRIX" SUBFORUM.