As the other person said, technically she has done nothing wrong.
Its very easy to fall into the trap of feeling like you want her back, when really what you want is the security of the relationship back. If i was ever told something, or two things actually that really worked in healing a break up, it was that
a) it really does get easier with time and
b) you need lots of friends around you, which is where i think you need to either find somebody you can spend lots of time with, can you go and see your family?
It might be a while before you can start seeing other girls, but obviously she finds this easier than you do. However, maybe she is spending time with him because as i said, you need friends around you.
You might think you want her back, but what was wrong with the relationship? Why did it end? Try to focus on these points and you might actually realise what you did was for the best, no relationship that is making you feel bad is one worth having.
I honestly do feel for you as i know it is so hard, because your entire lives were based around each other, thats why you need to spend time doing things, keeping busy, and you will start to get over her in time.
You say you don't know wether to break contact with her? Maybe its best to do that at the moment, until the time comes where she can tell you she's been with somebody else, and it doesn't hurt as much, because it will always hurt, let me tell you.
Please, please keep busy, and cry if you need to cry, don't hide anything. I'm here to talk to, i know it doesn't help much, but talking to somebody, even if its someone you've never met, is better than talking to nobody.