You know what?
The only person that can make you happy or sad is yourself. You decide it, whether to be happy or down. You decide it to yourself.
If someone make you sad and let you down. Don't be sad! Who they think they are?
If you are sad, they won and successful make you feel down. and you lose to them.
Why not you be strong and forget them. They just your scum in your life. Be friend with people that only support you and valued you.
If you fail in your exams, don't feel down or sad. Try again and study hard. If you let yourself down, you won't or never achieved success in your life. You will be a useless person for the rest of your life. Doesn't matter if you lose or fail many times, but never let yourself stop working. Keep moving and moving. Don't stop. Believe me, YOU will win one day.