That said I could be completely off the mark and bexause of Machida's advice she gets back with a terrible cheating boyfriend and has a miserable life.
I interpreted his advice as suggesting she's not over with him yet. In other words, she left him before she really wanted to leave him. That is, she left him while she still genuinely loved him, which is quite contradictory, although not unrealistic because humans are flawed creatures that can keep loving total monsters till the bitter end. But assuming she's not mentally ill, she could just stay with him until her love runs out for real, witnessing his bad sides. Then she could leave with no lingering emotions whatsoever, never looking back. She would be free to seek new love, without anything in her past bothering her.
Of course there's also the remote possibility the cheating dude would turn a new leaf.