Relationships and Love

Not a very dorky subject, but one that is going though my mind nonetheless. Why do we have them? If someone you love just leaves after two years you're crushed and they move on. Why do we allow ourselves to do that? I'm not sure but I think that it should be simpler. I'm also not sure how to make it simpler. It just has to be hard I guess, and that's not fair. We get into these relationships, knowing it'll probably end, but then we get so in love and so sure it'll last forever and then it's gone and our original thought comes true, and it hurts bad. All I can say is "love songs suck and fairy-tales aren't true" -thanks to Bowling For Soup!!