Human nature. The thing is, when confronted with conflict, or a bad situation, humans tend to rationalize it by blaming something, or someone. This can give them peace, piece of mind, or even a place to start to recover from. A classic example is how Adolf Hitler convinced a war-raveged, and financially crippled Germany, that their inordinate amount of misfortune was due to the Jews (among others).
As far as relationships go, in bad break ups specifically, both sides seek to blame someone. This is usually the other person, but some have been known to blame themselves.
And before anyone questions me, I'm not saying that this is necessarily a bad thing. Hell, in all seriousness, if I hadn't placed blame on my first girlfriend for cheating on me, the depression I was in might have killed me. To this day, I'm pretty sure I'd spit on her if she ever tried to talk to me again, but that's neither here, nor there.
Things are crazy right now (probably less now then they were, which is good). Just keep a level head and things will be okay. Whether his apology sticks or not, it should no longer matter.
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Okay, so anyone wanna tell me WHY I'm barely passing my Psychology courses?