<human>: Can you condense the text into a few key points?

So I recently went off to college in Germany, I had a very serious (so I thought) relationship with a guy for 2 years and then we were on and off for 3 years before that. I found out through a friend that he was dating some girl at his school behind my back. When I confronted him, he said "I didn't think it was relevant". What the hell is that?! I mean he was my first boyfriend in 8th grade, we were each other's first kisses. Naturally, as a girl who doesn't like being screwed over, I called him and ended it on the spot. Guys of Reddit, why would he do this to me? Got any advice? and to anyone, what should I do? Seriously, anyone who has been heartbroken knows all about the mood swings: depressions, anger, a "FUCK YEA" attitude, etc. It's causing my academics to suffer (I hate getting bad grades) and I find it hard to get close to anyone....I was always a good girlfriend, I mean, hell, we beat the Borderlands campaign mode and both reached the level cap (when it still was level 50) multiple times. I gave this guy EVERYTHING, and he just ripped my heart to pieces. I REALLY need some advice, I feel lost. I lost my best friend in the whole world and my chest physically hurts thinking about it. What do I do?
<bot>: Guy cheated on me, didn't tell me, broke my heart, I was a good girlfriend (I swear), I need advice.....