During a recent interview Jennifer Lopez mentioned that her break up with Alex had nothing to do with someone else, it had everything to do with her.
“things happen[ed]” and that’s when she realized she needed to take charge. “Once you get to the point where you’re like, ‘This is not right for me, or this doesn’t feel good, or I need to make an adjustment here,” she explained. “This is not really about anybody else but me.’ Once you do that, stuff starts falling into place.”
she also said happiness starts within.
She didn't mention Alex by name or mention her new relationship with Ben Affleck but that gives us a bit of an idea of why she called off their engagement. Also her saying it didn't have anything to do with someone else, could either mean maybe Alex didn't cheat or maybe she was referring to Alex himself.