Corship

So the situation is: I moved away from my home to be with my current girlfriend two cities away. She convinced me to connect with my ex because my ex was always a very good person to talk to and shes stronger than anyone I've met. and she wanted me to have a friend. I refused to for a long time but she finally got me to. Well, I started to feel those old feelings again with my ex, i started calling her more often and my girlfriend noticed how happy i was when i was talking to her. Well, the whole situation turned into a fight but i have it under control right now... But i still can't decide what to do. I don't want to hurt either of them, but i can't very well have them both. That spark with my current girlfriend seems to have faded a lot... I don't know if that something that happens and it comes back. I don't know who i feel for as a best friend and who i feel for as more... I usually don't have friends so the feeling for me is hard to separate. Oh, and I know it will be a question... but the reason my ex is my ex is because we met all the way back when i was in high school. I was thinking with something other than my brain and I kept leaving her for the chance to have more physical relationships... But I did repeatedly go back to her, something kept me going back. Please give me some input so I can hopefully figure this out... and just ask for additional info.