Really miss my Ex, but hate her at the same time?

[boy 1]

Basically we got together when I was 15 and she was 16, after a while we fell in love and had a great relationship. She was my best friend as well as my girlfriend and that worked both ways. Now after 3 1/2 years she out of the blue breaks up with me.

I treated her amazingly well throughout the relationship and was always there for her when she was having family issues, or friend problems. I bought her loads of presents including a surprise holiday which took me over a year to save for, bearing in mind this holiday was just over two months ago.
She relied on me so much and I saw her nearly everyday of my life, I gave up my friends for her, (which I know is very stupid of me). When I did have the chance to go out with friends she made me feel bad, and know how to make me stay in with her. She stopped me from going away with friends because she wanted me to be with her. But i just loved her sooo much I would've done anything for her.

In September we were both about to move away for University. I went first, and she wouldn't stop crying and left me loads of notes in my bags so that when I got there I knew she still was there. Throughout my first few weeks I had an amazing time, but knowing she was both home, I always made an effort to get in contact with her and see if she is ok.

Then she goes to university and again all seemed well we talked a lot, skyped each other, and after her being there for three weeks I decided to travel down to see her. All seemed well in my eyes and she was herself on the phone. It took me 10 hours to get there, and was greeted by her but something wasn't quite right and she wasn't herself towards me. I thought I will see how the weekend goes, but constantly she seemed more interested in her flatmates than me, it was awkward between us but that was down to her making no effort. Im about to leave hers that weekend and later I txt her asking why it was weird and different. Knowing I had a ten hour trip by myself she calls me to say she doesn't know if she wants to be in a relationship as she doesn't have time, which is a lame and pathetic excuse. And that she has been feeling like this for a couple of weeks. Which means after a week of university she made her mind up. Then I have to travel back by myself for ages knowing this. I kept trying to contact her in the first week even though she said not to. I didn't know what to do. But i logged into her fb and read messages. She was saying that she is fine to people and that 'I;m having a breakdown lol' and that her and her flatmates were laughing at my fb statuses. Also on twitter I see things talking about a couples cab ride with her, two boys and another girl. I can't help thinking she cheated on me and couldn't admit it or tell me, and has now got with someone else. This is just not her and she has changed into a bitch because she has a few friends and comes across popular for the first time in her life.
I haven't looked at her fb or twitter or tried to contact her for two weeks but still miss her so much and want her back. I wish she would realise what she has done and regret it. But she doesn't and she doesn't care at all it seems like. I can't get around how anyone can change that quickly and forget about me after so long together.
Even her friend said she has changed and it suspicious the way she is acting, and I can't get the thought of her with someone else out of my head. Her mum walked out of the family home two years ago and she has refused to talk to her mum since, so i know she can be very stubborn and won't get in contact with me, although her mum was in the wrong, and I've done nothing to deserve this.

I just am so lost and can't get my head around the situation. PLease help