I just found out shes pregnant, but im not in love with her anymore.?

So my ex girlfriend and I had been dating for about 6 months. Things werent working out for many reasons so i decided to end the relationship. This was about 2 weeks ago. I simply am not in love with her anymore and i really am not happy with her. Recently i have reconnected with a very old friend from highschool. There was always something between us even back in highschool but due to other relationships we both never pursued it. I honestly have been in love with this girl for so long and have always wanted to be with her. I always said that i would marry her someday and i meant it, and i know she feels the same way. So things with her and i have been great however my ex girlfriend dropped the news on me yesterday that she is pregnant. I honestly dont know what to do, i really dont want to be with her and im in love with somebody else. I am not a sbag and im prepared to do whatever i need to do to handle this, i just dont want this to put tension on the possibility of me and the other girl of getting together. Another factor is how young we are, im 20 and my ex is 18. My ex is very immature and irresponsible and this is one of the reasons we had problems. She has been drinkin HEAVILY the past couple weeks due to our breakup which i blame myslef for, but now thats shes pregnant it changes everything and i dont see her stopping drinking any time soon. I dont know what to do or think about any of this. Any kind of advice would be helpful.