The key to being happy is to take responsibility for your emotions.
It is so simple. If you want to be happy, be. It's not any one else's responsibility to make you happy. It is also not any one else's responsibility to make you not happy. You are the only one in charge of your feelings. Once you wrap your head around that very simple, very true fact, you can be happy. Or sad. Or mad. Or whatever you want, whenever you want.