[Eternal]

Hi there, I'm really sorry to hear that he left you like that. You're right, it completely isn't fair and he shouldn't have gotten into a relationship if he wasn't ready.
If you haven't already, it would be best to cut off contact with him, this will help you to move on. Distractions are also a great way to keep yourself busy. Partake in activities that make you happy to help keep your mood up. This can include sports, playing an instrument, spending time with friends or family, or any other hobbies you have.
You should also read This Article on breaking up, it has lots of helpful advice.
Lastly, remember that its going to take time. Right now is the worst that you are going to feel in all of this, so just keep your chin up and know that it will get easier. And on the bright side, the relationships over so now you can find a guy who will want to be with you and will treat you right.