Decent movie but I didn't buy them as a couple

Entertaining movie, but the problem is with the premise. If you can't buy the premise the rest of the movie just doesn't make sense. She is the manager of an art gallery and he gives tour guides on city buses? In what universe would these two be a couple? Maybe as a fling, but not buy a gorgeous condo together and potentially marry. This also makes me wonder who put up the money to buy and decorate this humongous beautiful apartment? Her? Him? Both? The family helped? He may be a popular bus tour guy but I'm not sure he would be bringing in that kind of cash. During the movie he even says he's busting his ass so eventually she won't have to work. What? I would think HER income far exceeded his. The fact that he was inappropriate, selfish and not interested in doing dishes would be beyond obvious from the beginning.

In the very beginning of the movie they showed a long montage of their life as a couple; doing all kinds of fun couple things together, travelling, laughing...and it looked like they had an amazing time together. But once the movie began there was no hint of how this could have been. I understand the movie is called "the break up" but I would have liked to have known HOW they got to be a fabulous couple in the first place because the montage was not enough to convince me that they previously were perfect for each other before they started to break up.