I used to love a game; now it just makes me angry.

It's natural. You developed a case of the cocky cunt syndrome, so you feel angry when someone kills you. Wondering.. "how did this happen?! statistically I should have killed them! (with no actual statistics) this is fucking bullshit!" It's normal. You probably aren't good at much else so it gets to your head for the first while, but you'll eventually learn to accept loss, and be calm. That is the key to winning and becoming better in the long run. Patience. If I lose a game, I accept it, and try to figure out what I did wrong to better benefit myself in the future. I always blame myself for a loss, never anyone else. ;)