Human emotions are HIGHLY controllable .. if you understand how they operate and learn how to reprogram them.
You can do this either through cognitive behavioral psychology or through the practices of Buddhism. CB psychology deals with ONE problem at a time .. Buddhism deals with all problems simultaneously. But both use the same basic principles .. they retrain your unconscious, and reframe your reality.
You don't control emotions by practicing to control them.
You control them by stepping slightly to one side, no longer resisting them, and letting them roll right by you.
Think of emotions as a freight train barreling down the track. If you stand ON the track, you will be run over. Even if you try to control that train by holding our you arms to stop it ... you will be run over.
Instead ... just take one step to the side, OFF the track, and watch that train roll right on by while you stand there, unhurt. This is NOT detachment. You do not build a wall around your feelings .. what you are doing, actually, is fully opening up to them. Allowing yourself to feel the craving and the pain and everything else you don't want. And when you feel these, you call up great compassion for this hurting creature, this You. Just as you call up great compassion for everyone else who hurts (and we all do).
Oddly enough, by opening up to our deepest fears ... they cease to push us.
Jealousy, anger and vengefulness are all attempts to NOT feel our pain, attempts to resist our pain. Things always hurt (both psychologically and physically) when you tense up and resist .. and when you are convinced that you should not be hurting.
There is only one way to learn THIS kind of observation, acceptance, and non-resistance .. and that is through the practices of Buddhism, starting with meditation.
Now, the Mahayana schools of Buddhism rely highly on the guidance of a teacher, in order to be effective.