Coping with failure

Fairly new player here, recently starting trying out AP Kennen in mid and while most games I'll dominate more and more often I'll get behind in CS, Harassed and then eventually killed. Basically from this point I usually try something desperate to get back in the game (which usually fails) or play defensive and let them snowball ahead, carry their team to victory and I feel terribly guilty and depressed for causing 4 other people to lose because I suck. Lately its been getting so bad that I have started just to leave games after I get a couple of kills down in mid because I just feel too terrible to stay playing the game.

TL;DR How do you cope when your fuck-ups cost a game?