Forget "I'll be happy when...". If you can't be happy when pursuing a goal you won't be happy when you achieved it.
Expectations cause a lot of unhappiness. Often we suffer because we believe a thought that argues with reality. Reality has no concept of that something "should" have happened or someone "should" have behaved a particular way. This is simply our own personal belief, that is creating a happiness gap between reality and our imagined reality.
You don't know your future. If you are pained by external things, it is not that they disturb you, but your judgement of them that disturbs you, and it is in your power to wipe out that judgement.
The story of the Chinese farmer:
Once upon a time there was a Chinese farmer whose horse ran away. That evening, all of his neighbours came around to commiserate. They said, “We are so sorry to hear your horse has run away. This is most unfortunate.” The farmer said, “Maybe.”. The next day the horse came back bringing seven wild horses with it, and in the evening everybody came back and said, “Oh, isn’t that lucky. What a great turn of events. You now have eight horses!” The farmer again said, “Maybe.”. The following day his son tried to break one of the horses, and while riding it, he was thrown and broke his leg. The neighbours then said, “Oh dear, that’s too bad,” and the farmer responded, “Maybe.”. The next day the conscription officers came around to conscript people into the army, and they rejected his son because he had a broken leg. Again all the neighbours came around and said, “Isn’t that great!” Again, he said, “Maybe.”.