We never want to hear those words that put blame elsewhere. What happens in a relationship is that one cares more than the other, and when those words hit the scene, we know it's like a red flag at a bull, saying "Hey it's really all your fault". "It's not you, it's me" works to reverse the psychological impact of a breakup, and is often used when the person saying it is too inadequate to explain exactly why the chemistry of the relationship didn't work.
actual meaning between the lines...
It's not you it's me, no really IT IS! It's ME who can't stand you, it's ME who wants you gone, it's ME who should be put in a straight jacket for being with you.
"Ada perkara yang kamu suka tetapi sebenarnya ia adalah keburukan buat kamu. Ada perkara yang kamu benci tetapi sebenarnya ia adalah kebaikan buat kamu"