Milk, peanut butter, tofu... Hopefully everything in your refridgerator, freezer, and pantry has an expiration date. In regards to food, expiration dates are important, good even. They keep us safe and healthy.
Other things have expiration dates as well. Utilities bills, foreclosure and eviction notices, and sometimes even lives. Whiles these are just as necessary, they are so much harder to cope with. You can't just throw them out when they go bad, go to the grocery store, and get a replacement.
Many relationships have expiration dates. It's hard to say whether or not those are the hardest kinds of expiration dates to deal with or not. At least there will always be the possibility of another one, and hopefully won't land you in a grave.
How are you supposed to let go? Each hug, each kiss, each simple touch... hurts. You miss them prematurely, you miss them when they are still in the seat next to you. How are you supposed to let yourself love them more and more each day until it ends? Is it worth the pain?
Regardless of how hard you try to hold on, sometimes you can't change the day it expires, just as you can't change the date on yogurt; it will go bad at the same time, no matter how hard you try.