Having a hard time getting over someone..

I wish I could rewind time, and make up with someone that I spent many an awesome time with last year.. but I can't. And it sucks.

My best friend told me that it'd get better, and I'd move past it, and it's his loss. But seriously, she's been my best friend for twenty years, she's a bit biased and is supposed to say stuff like that.

How do others in this situation move on, and forget about someone? I can't see how others do it, pretend that someone else just doesn't exist anymore and have no urge to talk to them or to try to make things better and move on.

Constructive suggestions are totally welcome...