People can fall out of love, it happens a lot.
It happen, yes. Despite all the efforts from both side, sometimes you're just not meant to be together. But if they loved at some time, they'll not cheat, they'll just break up.
By the way, people should stop to fear "I need a break". It doesn't necessarily mean that (s)he want to be with someone else, just to be somewhere else in order to question his/her feelings. And it doesn't imply that (s)he'll break up, you need to be deprived of something to understand how much you miss it, or not.
It's so easy to be annoyed by one's small habits, let it grow and end wanting to kill him/her. But doing so, you not necessarily fall out of love, you can just have forgot that you love. Being apart for few weeks, it's those small annoyance that you'll forget, rediscovering how much you love him/her through that void you feel in your heart.
Through fear, circumstance or a myriad of other reasons one party will start trying to make the other person leave them, rather than just leave themselves.
It's not a question of fear, it's a question of selfishness. If you loved him/her, you need to have come to hate him/her to want to act that way. This simply because the person you disrespect the most in such situation is not the other, it's yourself.
Note that this, as well as everything I said previously, is intended outside of abusive relationships. Here, yes, the victim will possibly cheat in order to looks unworthy to the eyes of his/her abuser. But it's a specific case since it was a one way love right from the starts.
Its a pattern repeated far to often to be considered 'rare'.
Is it really repeated this often?
And it's a legit question, because we always hear when a breakup is due to a drama, rarely when it isn't. Your co-worker or neighbour will tell you if (s)he cheated, but you'll discover one day that (s)he divorced three years ago, when (s)he'll tell you that (s)he'll remarry. And if (s)he don't talk about his/her second marriage, you can perfectly never know that the wife/husband (s)he talk about isn't the same that the one (s)he talked about years ago.