(Ex) Girlfriend wants sudden break up + acting strange

I had been with my girlfriend since January and everything was smooth up until mid september. A couple of weeks before I was going to be heading off to university she started to get worried that we won't be able to continue the relationship long distance. However, in the couple of weeks before I left we assured each other it will be fine and she eventually became satisfied that we can go on. Since then, I started uni on Sunday and everything was fine until Wednesday evening when she sent me a text completely out of the blue saying that she wanted to split up. I asked her why and all she replies is "Because I want to". From that point onwards she has hardly spoken to me, maybe a couple of texts a day and a few very short phonecalls. I have continued to ask her what's wrong and why she wants to split and she just says nothing.

What is going on and what am i supposed to do?

So she doesn't wanna say her reasons, let's guess! She got bored of the relationship which is a long-distance one? She doesn't develop anymore feeling towards you 'cause you two are so far apart? I'd say that feeling inside her had been declining.

Respect her decision. Then try to find another girl.

Her not giving you a good reason and saying 'because I want to' is just an easy way out for her. She is dealing with this situation in an immature way and to be honest it sounds like you could do better.

Live life, study hard and enjoy what Uni life brings :)