Happiness is not dependent on an event, it is an inner state of being that does not happen to you but that you must achieve. Happiness is not a happening that you wait to happen, it’s a choice you have to work at to achieve. Therefore you can always be happy, regardless of the events that are happening around you.
Fun is an event, not effecting your inner being. It is an occurrence that happens from time to time. It would be great if we were having fun while being happy. But life is sometimes no fun. It may even be very bitter and painful. However even in those times we can be happy. Fun is an occasional happening and event. Even if you could have fun everyday it would not necessarily make you happy.
The Torah teaches that the way to happiness is to choose the path of truth, apply your intelligence and skills to do the will of G-d. When the soul is in harmony with the whole divine symphony of life then it feels a deep and lasting happiness. When such a person experiences painful events, her inner constant state of happiness is untouched. Therefore the good person even when she encounters great suffering she is still in state of inner happiness. The evil person, however, chooses a life of dissonance. She is not interested in coordinating her actions with the values and ideals of G-d. Even if the evil person is having daily fun none of it effects her inner self that is actually broken and depressed.
The good person may have more painful events and yet be happy because she is committed to the ways of G-d to do His work on earth. The evil person, however, could be having a ball. She may be enjoying the party but when the music stops playing, when the game is over, when the fun ends her inner self is left impoverished. She is having fun but she is not happy.
You can HAVE fun but you can only BE happy.