I guess schadenfreude may be the cousin of "helper's high" even though the feeling of latter is something you get out of helping out. Envy is just human nature, the grass they say, always appear to be greener on the other side of the fence. People get envious of things they think their counterpart has accomplished or got that makes them better or superior. However, some do not make any effort to cause harm to such an individual. It becomes something evil when you put in some machinations to cause hurt to the envied person.