A wise friend once told me, "Don't hate, congratulate." -- Jealousy is an ugly monster and serves no useful purpose. Never give into the temptation to be jealous. It's a complete waste of time. Happiness is contagious. You can give it to someone else, but you can also get it from someone. It doesn't matter the origin... just get some. You are in complete control of your emotions. You can make a choice and to ignore or feed a feeling you are experiencing. I don't give much credence to my emotions. They are too unpredictable. They can be affected by the amount of sleep I've had, or what I ate for lunch.
Choose happiness... and if you can't find some for yourself, share someone else's. Be happy for people. Congratulate them on accomplishments. Share in their joy until you can find a reason to celebrate for yourself. It's not difficult. Make the choice.
Happiness is all around you... if you are brave enough to look beyond your own circumstances. But I must warn you... you are also surrounded by sadness. And while I'm not asking you to ignore someone else's plight (on the contrary, we should all be empathetic) focus on the positive, whether it be in your own life or someone else's blessings.