In my experience, when your significant other says something along the lines of "It's not you, it's me", it means that the relationship is over. Gone with the wind, so to speak.
It also comes to my attention that the human heart involuntarily races during the time immediately following those dreaded words. Breathing becomes hitched, tear ducts begin to excrete a salty substance, and one tunes out most of what is going on around them. Even if the breakup isn't official at that point, "It's not you, it's me" pretty much seals the deal.
Ah, the unforgiving nature of a relationship. Fluxuating feelings of insecure and emotionally perturbed beings jeopardize the success of happy and doubtless involvement with others of the same species. Emotion, playing a large role in the success of said involvement, quickly takes over human logic during a breakup. Intelligent thoughts escape even the most experienced of humanity, and thus results in use of an overused cliché.
Goodness knows the vulnerability of the fragile human race; yet time will heal all wounds.