Mixed Feelings For Girl?

Sorry if this is a bit long but please read .....Well this girl went to my school and we never spoke but we started speaking to each other through friend, and now we speak nearly everyday :) and she said she liked me and wanted to go out with me ... but i couldn't cause I loved this other girl :/ but i dont like her anymore and I dunno if I wanna be with the girl I never spoke to , and shes got a boyfriend at the moment and I know she loves me , its just do I want to be with her .. I get jealous when she goes somewhere with her boyfriend because hes a nob and treats her badly but he sez he loves her!!! but I know she would dump him for me I just know it ! and I love her with all my heart and I just want her to be happy :( but I dunno being with me would make her happy .. please give me some guidance or help on what to do