Most Helpful Girl
Aw bless you, it sounds like you are quite young, which is good and I can tell you what I have experienced. I have recently been through the same thing, I know it sucks.
To put it simply this guy is a jerk. Why? Because he was dating her when he was with you. How dare somebody treat you like that. I am telling you now this relationship with this girl won't last because this guy is just messing around. Men do not mature until at least 27-28 and generally are not looking to stay with the same girl.
He has not valued you or respected your feelings at all which tells me he is immature, and a waste of your precious time.
You deserve someone better and someone that matches you.
Now here is what you do, right now. Go onto Facebook and delete him. I know it is drastic but constantly being updated on how amazing his life is with her is only going to keep putting you through a vicious cycle of pain. Trust me, been there, done that, got the t-shirt. I had to do it with my ex and I was a lot better off for it. Cut him out of your life right now. Delete his number, delete emails, delete all text messages.
Think about you now, and please do not blame yourself for not being able to keep him. Let yourself heal. Write yourself a list of all things you have wanted to do in life whether they be big or very little write them all down. Focus on completing one of these things each day. Could be having a hot chocolate or writing a story or designing a website.
In addition another tip, help others that need you. There are people out there that are suffering from all sorts of things and need someone to show them some kindness. I started volunteering after my break up and helping others changed my perspective on life. I was too busy trying to please these guys all the time that treated me like dirt, and I realized I had valued gifts that were being put to waste, where my time could be better spent helping others.
Now tell yourself everyday, I'm a lovely, beautiful, charming, intelligent girl. Act with grace and maturity something your ex clearly does not have. Have fun. Stop thinking about him, think about you! :)