Umm, i need girl help.?

Okay, i've known this girl for 3 years now. we're best friends and early this summer, we started getting sooo close. And we were exchanging poems and talking nonstop. My poems were about her. How i felt about her. and Her's were about herself. And long story short, she said she loved some guy named doug from her childhood. that they talk everynight, after me and her talk. This was a huge surprise and i stopped talking to her for a month. Then i talked to another girl, (i'll call her jessica so you arnt confused) and it got me to forget her. Schools about to start. We have 4 cles in common. I am going to see her everyday. And I called her yesterday and we're talking again. I am starting to fall for her again. I am with the other girl. How can i be falling for her again, when i will just end up hurting Jessica. Jessica wasnt much of my type, the other girl is. the other girl has so many problems, but i just want to be there to help her through it, but she told me i deserve better. (what did she mean by that?) and i cant stop thinking of her now. And i dont know what to do now.