They say it lasts forever. Well, I am kinda agree about it.
Forever in maybe we'll laugh everything about it, if somehow we are reminded of it, giggle our foolishness and wonder how we could do such a silly things, like obsessed with some (called cool) boys (or girls). Forever in someday we're going to tell our story to our children, and grandchildren, and make sure that they won't repeat the same mistakes, like we did.
We fell in love, then we leave, found another leave, then leave. It's beautiful to have all the stories, because (I think I've said it before), we can forget names, places, time, but we can't forget feeling. The beautiful feeling that we had it before, it still feels beautiful right, even when we don't have it anymore.
So, it doesn't mean you're unfaithful, when you say it lasts forever. It's like we remove a file in a recycle bin, it's there, but we don't need it anymore. :D