There's always a time in life where you'll be forced to let something or someone go. Either they're going to move to another city, or they pass away, or maybe something more complex could happen. I don't know. The thing is, shit happens, and you have to learn how to let go, stress is the last thing you want to feel.
First of all, you have to admit, you had a good run. Everybody has good and bad moments with other people they care about. If you didn't have any moments with someone, that's because you don't care about that person and you'll get over it very quickly. The more you care about somebody, the more you'll have trouble letting go.
Another thing you can do is stay in touch. The thing about it, though, is that it becomes less frequent over time. You'll forget that the other person is even there, but of course, it does help to stay in touch the first days. That way, the process of letting go is more gradual.
So, let's say a person's deceased. If you put emotions into objects, then you're going to have a hard time, but if you don't, it's going to be very easy. My grandmother, when she lost her husband, started selling his stuff. It was hard for her, but she needs the money, and there's always some emotional bearing in keeping around the shoes he always used, his clothes, etc. Heirlooms, of course, she wouldn't get rid of, but you have to get rid of the things that didn't matter, if you don't, they'll just be there to remind you of the other person every five minutes.
The last thing you should do is say goodbye one last time. It helps a lot. How come? Because, that way, you know you're ready for bigger, better things, and that there's nothing that can hold you back, especially the past. Remember, to never turn back, because something might be lingering. This is the Eccentric Realist signing off for today, see ya whenever I get the chance to post again...