Why....

Why do all good things have to come to an end? It seems like nothing good is ever here to stay ... there is one thing, or one person I guess, I want as a permanent fixture in my life.... and, once in a while I get a glimpse into what would happen if that came true, and it is so amazing... the up and the downs... it is what makes me happy, then it always comes to and end and that person goes away and it is another month or so before I get  to enjoy this again... 

Why do good things always have to come to an end?