looking for an answer.. Options

[Terror]

Ok, I'm not even sure I'm supposed to be posting in this place, I dont care if you delete this topic--but I really need some answers.

Ok, first of all, since my problem is about a girl, I figured GIRLS would be most helpful, seeing as most guys are absolutely dee-dee-dee when it comes to relationships.
Ok, so to the point.
I met my ex girlfriend in 6th grade, she moved away, I continued living there for a few years, then I met her again in 8th grade.
We started going out. I realize theres alot of people arguing that 15 year old's dont know what love is, but whatever--THAT, that was love. No f**king doubt in my mind.
I fell completely for her. Absolutely and totally devoted to this one girl.
She was perfect to me, abso-f**king-lutely perfect. A few months in, I thought it would make her happy to give her a ring for our 6th month anniversary.
So, I got a job, babysat, mowed the lawn, in short, I broke my goddamn back and managed to get around 750 dollars. I went to a jewlerers, and got her the prettiest ring I could get her with 750 dollars, then I gave it to her. I like, kinda proposed half jokingly to her, like "Danielle, would you marry me?"
But then I saw her reaction, and I was actually shocked.
So we were engaged.
I bought her a necklace sometime later, (which wasn't cheap by the way)
Months passed by filled with so much love and happiness I probaly should have died then, cause I don't think I can experience uplifting joy like that ever again.
I wrote her poems every single week. Everytime we met I kissed her on the cheek.

Sex wasn't even on my mind, cuddling was enough for me.
We were perfect.
I loved her.
She loved me.
Then I found out, the day before my birthday and a few days before our one year anniversary, that she's been cheating on my, the.WHOLE.damn.time.
She's had sex with two other guys, and was messing around with a few others.
I won't delve into all the melodramatic weeks that followed, but to say the least, my world fell apart, cried for days on end, and so on.
Now, I come here, just wanting to know, was there anything I did wrong?
I mean, If I could I'd have given the world to this girl, and I tried.
I didn't even look at a girl twice for nearly a year, she was my life.

So...yeah, thats pretty much it.
And all I want to know, if theres ANYTHING you think I could've did better, or something I did wrong.
I'm just looking for answers.

-Sorry for being so long...and thanks to anyone who helps.

Then, I found out

[BryMonster]

You did nothing wrong. If anything, you
were being the sweetest boyfriend possible.
Sometimes girls think to themselves ,"He's
too good for me." I know this, because I've
been given that as a lame excuse. Probably
that's why girls cheat. Was there any sign
the entire time, that she was giving you a
bad vibe or something?