Doomed?

Does a relationship have to last until death to be considered successful? Does a break-up equal failure? Why do we look at romantic (or possibly platonic) relationships like this? Who set that standard?

If two people enjoy their time together, even for only a short while, does their separation define the entire history of the relationship? Are all the good times wiped out by the pain of the break up?

Can't we look at each experience in love not just as failures building up to something greater, but as great experiences that are worthy of our remembrance and consideration based upon their own merit?