Feeling terrible after a loss is a good thing
If you don't cry after the defeat soon appears, then you will never improve as a LoL player. I went from 36 wins over losses to 21. A cycle that had never felt worse in my life, however after I vowed to never lose a game the rest of the day again I went to 26 wins while my last game was 10/1/6 with over 180 CS in 20 minutes. Now I'm steadily climbing again.