Maybe today I am happy tomorrow everything can break. Beloved can die leaving you. Or worse you can have an accident become mentally disabled alzheimer. In this life there is nothing but loss to be experienced and passed on to your descendants. What is all this existence. What is this reality of infinite suffering?
I believe Buddha asked much the same questions. Then he sat under a tree for days (weeks?) and became enlightened.
Then there was the Schopenhauer. He neither became enlightened, nor killed himself. He lived until he reached 72!!!. How pathethic is that, given his philosophy?! I judge him.
Then there was Nietzche. He said that if you stare too long/hard into the abyss, the abyss will stare back into you. Went mad. The man
lived his words, i love him for that, among other things.
And, lastly, for the sake of objectivity, what you wrote also sounds exactly like the thoughts one has while in the middle of a depressive episode.
Which leads me to the question - was Buddha depressed?