Here's my story: I'm 17 years old now. I haven't really had any girlfriends yet cause I'm waiting for that special someone. I'm also what you could call shy, but once I get to know you I'm fine. It's just starting up a conversation with someone that I don't really know I find a little awkward cause I don't really know what to say. I'm the kind of guy that wants to get to know someone really well before I'll even bring up the idea of dating. A little while ago, there was a girl that I like enough to possibly be with but when I finally got brave enough to ask if she would be interested, I found out that she had just gotten together with someone else and they are still together so I just forgot about my feelings I had for her, which wasn't very easy to do, but I did. That was probably a year and a half ago. Now I think I might have found that special someone, but there's a catch, she has a boyfriend already. We have been very good friends since I moved to this school in second grade so I know everything about her. But a few months ago, I started to feel differently about her, and at the time she was single because her current boyfriend had cheated on her. But I just kept putting off telling her how I feel and now she got back together with her old boyfriend that had cheated on her. I mentioned before that I'm waithing for that special someone and that I'm the kind of guy that wants to know someone very well before dating them, and now I know I've found that person. For some reason all of the sudden I just started to feel differently about her. If a day goes by that I don't see her, I'll have to call her just to talk to her cause I miss her so much. Or if I'm in a bad mood at school and even if we just pass by each other in the hall and only say hi, it just makes me so happier. I don't even really know how to explain how I feel about her. I think I love her. I'm also the kind of person that can't stand people who cheat. I've thought about telling her lately but that's what's keeping me from doing it.

Here are the questions that I have:

Do relationships usually last when one of them cheat on the other and then they break up but then get back together?

Am I doing the right thing by not telling her how I feel?

Should I try to move on? And if so what are some things I can do to get her off my mind because I've tried to move on but I just can't.

To begin with... this happens to A LOT of guys... what I mean is, "falling" for a good friend of yours - heck, even your best friend... You get along great, she's attractive.. you feel she could have even been one of the guys.. It would make sense for you two to date, right?
WRONG.
We always fall into this trap.. females think differently (yes they fall for their guy friends too), but usually once you're in the friends zone its very hard to get out.
Now that we've cleared that out of the way:
The question you later ask is, whether it works out or not after one of the two has cheated.. Well - it's a very general question and it depends on the individuals involved.. But the answer to YOUR question is the following, It shouldn't matter whether it would work out or not. Because you can't sit there and wait for her to realize it's a mistake, or for HIM to cheat on HER again so then she's available and you sweep her off her feet...
Imagine that happens.. do you really want to be with someone, who is only going out with YOU because she got cheated on? You deserve better man.
For now-yes you are.. She has a boyfriend.. theres no reason to mess things up.. maybe in the gap where she was single you could have done something.. But imagine if you were that guy who is going out with her now, and some one just came in the middle of things and tried to ruin it.. Not-cool.
On the plus side though- you're still young, you'll meet a lot more girls.. You might think you love her, but like most people later find out.. things always seem better in your head than they really are..
Take it easy man.. You'll get your chance.. You said it yourself, you're shy.. It's not a bad thing.. but I'm sure if you tried to meet more girls out there- you would find a lot more that could compete with this girl that's taken.. dont you think?
There's more fish in the sea for everyone.. there isn't only one person in the world that can make you happy.. Just don't rush things.. go with the flow and things will fall into place for you..
I hope this helps.

Here are the questions that I have:

Do relationships usually last when one of them cheat on the other and then they break up but then get back together?
In high school it happens all the time.
Am I doing the right thing by not telling her how I feel?
Keep it to yourself because all her romantic attention is on someone else.
Should I try to move on? And if so what are some things I can do to get her off my mind because I've tried to move on but I just can't.
Hard as it seems you can move on, by not being around so much and talking and enjoying other people. Click on the links in my signature for some good insights into how to move on. Staying out of her business would help a lot.