Impossible love?

Hello everyone,

This is a pretty complicated and long story but please bear with me.

About 6 years ago, when I was about 13, I was in a relationship with a girl which I was really in love with. I felt like we fit together perfectly. I was pretty shy and she took more initiative. We liked the same things and we always had fun together. But after 2-3 years, she broke up with me because she saw me more as a friend. I was devastated and couldn't sleep for nights, though towards her and my friends I acted like I was fine. The next months, we pretty much ignored each other. We occasionally said hi but it always felt really awkward.

After a while I got used to it though, and we started to become friends again. She had a new boyfriend, but he was really nice and it was fun doing things together (in a group of other people). For a while I was okay with this, I saw her as a friend too now. But after a while I started to get feelings for her again. It felt like she liked me more than her other male friends (probably because we've known each other for 14 years now). But by now her and her new boyfriend had been in a relationship for about a year.

As I said, I'm a shy person and I don't express my feelings that much. For this reason (and because she had a boyfriend) I never dared to tell her how I felt. I was afraid she would think I was crazy for still loving her after all that time.

Now she is still dating the same guy (for about 2 years) and she will move to a different country really soon. Yesterday she had a going away party and I hugged her and said goodbye. Now I feel almost the same as when we had just broken up, really depressed and powerless.

I really don't know what to do. I always thought she was The One, but I absolutely blew it by being too passive. Of course it would be really unrealistic that she will instantly break up with her boyfriend and stay here, but I can't help but think about it. I feel more than ever like I should tell her, so at least she knows.

Please tell me what I should do, any advice is appreciated.

Thanks.

Edit: might be good to know these things:
I am 18 now.
We never went further than kissing, I was to insecure to go further.
I have never dated anyone else.
If you need to know more, please ask.