What are these second thoughts I am having?

Why does what was beautiful suddenly shatter in hindsight because it concealed dark truths? Because such a situation makes it impossible to be happy? But we were happy! Sometimes the memory of happiness cannot stay true because it ended unhappily. Because happiness is only real if it lasts forever? Because things always end painfully if they contained pain, conscious or unconscious all along? But what is unconscious, unrecognized pain?